diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractValueUsageTransformer.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractValueUsageTransformer.kt
new file mode 100644
index 00000000000..652509b9534
--- /dev/null
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/AbstractValueUsageTransformer.kt
@@ -0,0 +1,284 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.common.lower
+
+import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
+import org.jetbrains.kotlin.ir.expressions.*
+import org.jetbrains.kotlin.ir.expressions.impl.IrStringConcatenationImpl
+import org.jetbrains.kotlin.ir.symbols.IrConstructorSymbol
+import org.jetbrains.kotlin.ir.symbols.IrReturnTargetSymbol
+import org.jetbrains.kotlin.ir.symbols.IrReturnableBlockSymbol
+import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
+import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
+import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
+
+
+/**
+ * Transforms expressions depending on the context they are used in.
+ *
+ * The transformations are defined with `IrExpression.use*` methods in this class,
+ * the most common are [useAs], [useAsStatement], [useInTypeOperator].
+ *
+ * NOTE: Transformer is copied from Kotlin/Native with minor modifications
+ *
+ * TODO: the implementation is originally based on [org.jetbrains.kotlin.psi2ir.transformations.InsertImplicitCasts]
+ * and should probably be used as its base.
+ *
+ * TODO: consider making this visitor non-recursive to make it more general.
+ */
+abstract class AbstractValueUsageTransformer(
+    protected val irBuiltIns: IrBuiltIns
+) : IrElementTransformerVoid() {
+
+    protected open fun IrExpression.useAs(type: IrType): IrExpression = this
+
+    protected open fun IrExpression.useAsStatement(): IrExpression = this
+
+    protected open fun IrExpression.useInTypeOperator(operator: IrTypeOperator, typeOperand: IrType): IrExpression =
+        this
+
+    protected open fun IrExpression.useAsValue(value: IrValueDeclaration): IrExpression = this.useAs(value.type)
+
+    protected open fun IrExpression.useAsArgument(parameter: IrValueParameter): IrExpression =
+        this.useAsValue(parameter)
+
+    protected open fun IrExpression.useAsDispatchReceiver(expression: IrFunctionAccessExpression): IrExpression =
+        this.useAsArgument(expression.symbol.owner.dispatchReceiverParameter!!)
+
+    protected open fun IrExpression.useAsExtensionReceiver(expression: IrFunctionAccessExpression): IrExpression =
+        this.useAsArgument(expression.symbol.owner.extensionReceiverParameter!!)
+
+    protected open fun IrExpression.useAsValueArgument(
+        expression: IrFunctionAccessExpression,
+        parameter: IrValueParameter
+    ): IrExpression =
+        this.useAsArgument(parameter)
+
+    private fun IrExpression.useForVariable(variable: IrVariable): IrExpression =
+        this.useAsValue(variable)
+
+    private fun IrExpression.useForField(field: IrField): IrExpression =
+        this.useAs(field.type)
+
+    protected open fun IrExpression.useAsReturnValue(returnTarget: IrReturnTargetSymbol): IrExpression =
+        when (returnTarget) {
+            is IrSimpleFunctionSymbol -> this.useAs(returnTarget.owner.returnType)
+            is IrConstructorSymbol -> this.useAs(irBuiltIns.unitType)
+            is IrReturnableBlockSymbol -> this.useAs(returnTarget.owner.type)
+            else -> error(returnTarget)
+        }
+
+    protected open fun IrExpression.useAsResult(enclosing: IrExpression): IrExpression =
+        this.useAs(enclosing.type)
+
+    protected open fun IrExpression.useAsVarargElement(expression: IrVararg): IrExpression = this
+
+    override fun visitPropertyReference(expression: IrPropertyReference): IrExpression {
+        TODO()
+    }
+
+    override fun visitLocalDelegatedPropertyReference(expression: IrLocalDelegatedPropertyReference): IrExpression {
+        TODO()
+    }
+
+  //  override fun visitFunctionReference(expression: IrFunctionReference): IrExpression {
+  //      TODO()
+  //  }
+
+    override fun visitFunctionAccess(expression: IrFunctionAccessExpression): IrExpression {
+        expression.transformChildrenVoid(this)
+
+        with(expression) {
+            dispatchReceiver = dispatchReceiver?.useAsDispatchReceiver(expression)
+            extensionReceiver = extensionReceiver?.useAsExtensionReceiver(expression)
+            for (index in descriptor.valueParameters.indices) {
+                val argument = getValueArgument(index) ?: continue
+                val parameter = symbol.owner.valueParameters[index]
+                putValueArgument(index, argument.useAsValueArgument(expression, parameter))
+            }
+        }
+
+        return expression
+    }
+
+    override fun visitBlockBody(body: IrBlockBody): IrBody {
+        body.transformChildrenVoid(this)
+
+        body.statements.forEachIndexed { i, irStatement ->
+            if (irStatement is IrExpression) {
+                body.statements[i] = irStatement.useAsStatement()
+            }
+        }
+
+        return body
+    }
+
+    override fun visitContainerExpression(expression: IrContainerExpression): IrExpression {
+        expression.transformChildrenVoid(this)
+
+        if (expression.statements.isEmpty()) {
+            return expression
+        }
+
+        val lastIndex = expression.statements.lastIndex
+        expression.statements.forEachIndexed { i, irStatement ->
+            if (irStatement is IrExpression) {
+                expression.statements[i] =
+                        if (i == lastIndex)
+                            irStatement.useAsResult(expression)
+                        else
+                            irStatement.useAsStatement()
+            }
+        }
+
+        return expression
+    }
+
+    override fun visitReturn(expression: IrReturn): IrExpression {
+        expression.transformChildrenVoid(this)
+
+        expression.value = expression.value.useAsReturnValue(expression.returnTargetSymbol)
+
+        return expression
+    }
+
+    override fun visitSetVariable(expression: IrSetVariable): IrExpression {
+        expression.transformChildrenVoid(this)
+
+        expression.value = expression.value.useForVariable(expression.symbol.owner)
+
+        return expression
+    }
+
+    override fun visitSetField(expression: IrSetField): IrExpression {
+        expression.transformChildrenVoid(this)
+
+        expression.value = expression.value.useForField(expression.symbol.owner)
+
+        return expression
+    }
+
+    override fun visitField(declaration: IrField): IrStatement {
+        declaration.transformChildrenVoid(this)
+
+        declaration.initializer?.let {
+            it.expression = it.expression.useForField(declaration)
+        }
+
+        return declaration
+    }
+
+    override fun visitVariable(declaration: IrVariable): IrVariable {
+        declaration.transformChildrenVoid(this)
+
+        declaration.initializer = declaration.initializer?.useForVariable(declaration)
+
+        return declaration
+    }
+
+    override fun visitWhen(expression: IrWhen): IrExpression {
+        expression.transformChildrenVoid(this)
+
+        for (irBranch in expression.branches) {
+            irBranch.condition = irBranch.condition.useAs(irBuiltIns.booleanType)
+            irBranch.result = irBranch.result.useAsResult(expression)
+        }
+
+        return expression
+    }
+
+    override fun visitLoop(loop: IrLoop): IrExpression {
+        loop.transformChildrenVoid(this)
+
+        loop.condition = loop.condition.useAs(irBuiltIns.booleanType)
+
+        loop.body = loop.body?.useAsStatement()
+
+        return loop
+    }
+
+    override fun visitThrow(expression: IrThrow): IrExpression {
+        expression.transformChildrenVoid(this)
+
+        expression.value = expression.value.useAs(irBuiltIns.throwableType)
+
+        return expression
+    }
+
+    override fun visitTry(aTry: IrTry): IrExpression {
+        aTry.transformChildrenVoid(this)
+
+        aTry.tryResult = aTry.tryResult.useAsResult(aTry)
+
+        for (aCatch in aTry.catches) {
+            aCatch.result = aCatch.result.useAsResult(aTry)
+        }
+
+        aTry.finallyExpression = aTry.finallyExpression?.useAsStatement()
+
+        return aTry
+    }
+
+    override fun visitVararg(expression: IrVararg): IrExpression {
+        expression.transformChildrenVoid(this)
+
+        expression.elements.forEachIndexed { i, element ->
+            when (element) {
+                is IrSpreadElement ->
+                    element.expression = element.expression.useAs(expression.type)
+                is IrExpression -> {
+                    expression.putElement(i, element.useAsVarargElement(expression))
+                }
+            }
+        }
+
+        return expression
+    }
+
+    override fun visitTypeOperator(expression: IrTypeOperatorCall): IrExpression {
+        expression.transformChildrenVoid(this)
+
+        expression.argument = expression.argument.useInTypeOperator(expression.operator, expression.typeOperand)
+
+        return expression
+    }
+
+    override fun visitFunction(declaration: IrFunction): IrStatement {
+        declaration.transformChildrenVoid(this)
+
+        declaration.valueParameters.forEach { parameter ->
+            val defaultValue = parameter.defaultValue
+            if (defaultValue is IrExpressionBody) {
+                defaultValue.expression = defaultValue.expression.useAsArgument(parameter)
+            }
+        }
+
+        declaration.body?.let {
+            if (it is IrExpressionBody) {
+                it.expression = it.expression.useAsReturnValue(declaration.symbol)
+            }
+        }
+
+        return declaration
+    }
+
+    override fun visitStringConcatenation(expression: IrStringConcatenation): IrExpression {
+        expression.transformChildrenVoid()
+        if (expression is IrStringConcatenationImpl) {
+            for ((i, arg) in expression.arguments.withIndex()) {
+                expression.arguments[i] = arg.useAs(irBuiltIns.anyNType)
+            }
+        }
+        return expression
+    }
+
+    // TODO: IrEnumEntry?
+
+}
+
diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/InlineClassDeclarationLowering.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/InlineClassDeclarationLowering.kt
new file mode 100644
index 00000000000..c6a10ebc4ba
--- /dev/null
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/InlineClassDeclarationLowering.kt
@@ -0,0 +1,263 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.backend.common.lower
+
+import org.jetbrains.kotlin.backend.common.BackendContext
+import org.jetbrains.kotlin.backend.common.ClassLoweringPass
+import org.jetbrains.kotlin.backend.common.FileLoweringPass
+import org.jetbrains.kotlin.backend.common.descriptors.WrappedSimpleFunctionDescriptor
+import org.jetbrains.kotlin.backend.common.ir.copyTo
+import org.jetbrains.kotlin.descriptors.Modality
+import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.builders.*
+import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.declarations.impl.IrFunctionImpl
+import org.jetbrains.kotlin.ir.expressions.*
+import org.jetbrains.kotlin.ir.symbols.IrFunctionSymbol
+import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
+import org.jetbrains.kotlin.ir.symbols.impl.IrSimpleFunctionSymbolImpl
+import org.jetbrains.kotlin.ir.types.toKotlinType
+import org.jetbrains.kotlin.ir.util.*
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
+import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
+import org.jetbrains.kotlin.name.Name
+
+private const val INLINE_CLASS_IMPL_SUFFIX = "-impl"
+
+// TODO: Support incremental compilation
+class InlineClassLowering(val context: BackendContext) {
+    private val transformedFunction = mutableMapOf<IrFunctionSymbol, IrSimpleFunctionSymbol>()
+
+    val inlineClassDeclarationLowering = object : ClassLoweringPass {
+        override fun lower(irClass: IrClass) {
+            if (!irClass.isInline) return
+
+            irClass.transformDeclarationsFlat { declaration ->
+                when (declaration) {
+                    is IrConstructor -> listOf(transformConstructor(declaration))
+                    is IrSimpleFunction -> transformMethodFlat(declaration)
+                    is IrProperty -> listOf(declaration)  // Getters and setters should be flattened
+                    is IrField -> listOf(declaration)
+                    is IrClass -> listOf(declaration)
+                    else -> error("Unexpected declaration: $declaration")
+                }
+            }
+        }
+
+        private fun transformConstructor(irConstructor: IrConstructor): IrDeclaration {
+            if (irConstructor.isPrimary) return irConstructor
+
+            // Secondary constructors are lowered into static function
+            val result = transformedFunction.getOrPut(irConstructor.symbol) { createStaticBodilessMethod(irConstructor).symbol }.owner
+            val irClass = irConstructor.parentAsClass
+
+            // Copied and adapted from Kotlin/Native InlineClassTransformer
+            result.body = context.createIrBuilder(result.symbol).irBlockBody(result) {
+
+                // Secondary ctors of inline class must delegate to some other constructors.
+                // Use these delegating call later to initialize this variable.
+                lateinit var thisVar: IrVariable
+                val parameterMapping = result.valueParameters.associateBy { it ->
+                    irConstructor.valueParameters[it.index].symbol
+                }
+
+                (irConstructor.body as IrBlockBody).statements.forEach { statement ->
+                    +statement.transform(object : IrElementTransformerVoid() {
+                        override fun visitDelegatingConstructorCall(expression: IrDelegatingConstructorCall): IrExpression {
+                            expression.transformChildrenVoid()
+                            return irBlock(expression) {
+                                thisVar = irTemporary(
+                                    expression,
+                                    typeHint = irClass.defaultType.toKotlinType(),
+                                    irType = irClass.defaultType
+                                )
+                            }
+                        }
+
+                        override fun visitGetValue(expression: IrGetValue): IrExpression {
+                            expression.transformChildrenVoid()
+                            if (expression.symbol == irClass.thisReceiver?.symbol) {
+                                return irGet(thisVar)
+                            }
+
+                            parameterMapping[expression.symbol]?.let { return irGet(it) }
+                            return expression
+                        }
+
+                        override fun visitReturn(expression: IrReturn): IrExpression {
+                            expression.transformChildrenVoid()
+                            if (expression.returnTargetSymbol == irConstructor.symbol) {
+                                return irReturn(irBlock(expression.startOffset, expression.endOffset) {
+                                    +expression.value
+                                    +irGet(thisVar)
+                                })
+                            }
+
+                            return expression
+                        }
+
+                    }, null)
+                }
+                +irReturn(irGet(thisVar))
+            }
+
+            return result
+        }
+
+
+        private fun transformMethodFlat(function: IrSimpleFunction): List<IrDeclaration> {
+            // TODO: Support fake-overridden methods without boxing
+            if (function.isStaticMethodOfClass || !function.isReal)
+                return listOf(function)
+
+            val staticMethod = createStaticBodilessMethod(function)
+            transformedFunction[function.symbol] = staticMethod.symbol
+
+            // Move function body to static method, transforming value parameters and nested declarations
+            function.body!!.transformChildrenVoid(object : IrElementTransformerVoid() {
+                override fun visitDeclaration(declaration: IrDeclaration): IrStatement {
+                    declaration.transformChildrenVoid(this)
+
+                    // TODO: Variable parents might not be initialized
+                    if (declaration !is IrVariable && declaration.parent == function)
+                        declaration.parent = staticMethod
+
+                    return declaration
+                }
+
+                override fun visitGetValue(expression: IrGetValue): IrExpression {
+                    val valueDeclaration = expression.symbol.owner as? IrValueParameter ?: return super.visitGetValue(expression)
+
+                    return context.createIrBuilder(staticMethod.symbol).irGet(
+                        when (valueDeclaration) {
+                            function.dispatchReceiverParameter, function.parentAsClass.thisReceiver ->
+                                staticMethod.valueParameters[0]
+
+                            function.extensionReceiverParameter ->
+                                staticMethod.extensionReceiverParameter!!
+
+                            in function.valueParameters ->
+                                staticMethod.valueParameters[valueDeclaration.index + 1]
+
+                            else -> return expression
+                        }
+                    )
+                }
+            })
+
+            staticMethod.body = function.body
+
+            if (function.overriddenSymbols.isEmpty())  // Function is used only in unboxed context
+                return listOf(staticMethod)
+
+            // Delegate original function to static implementation
+            function.body = context.createIrBuilder(function.symbol).irBlockBody {
+                +irReturn(
+                    irCall(staticMethod).apply {
+                        val parameters =
+                            listOf(function.dispatchReceiverParameter!!) + function.valueParameters
+
+                        for ((index, valueParameter) in parameters.withIndex()) {
+                            putValueArgument(index, irGet(valueParameter))
+                        }
+
+                        extensionReceiver = function.extensionReceiverParameter?.let { irGet(it) }
+                    }
+                )
+            }
+
+            return listOf(function, staticMethod)
+        }
+    }
+
+    val inlineClassUsageLowering = object : FileLoweringPass {
+
+        override fun lower(irFile: IrFile) {
+            irFile.transformChildrenVoid(object : IrElementTransformerVoid() {
+
+                override fun visitCall(call: IrCall): IrExpression {
+                    call.transformChildrenVoid(this)
+                    val function = call.symbol.owner
+                    if (
+                        function.isDynamic() ||
+                        function.parent !is IrClass ||
+                        function.isStaticMethodOfClass ||
+                        !function.parentAsClass.isInline ||
+                        (function is IrSimpleFunction && !function.isReal) ||
+                        (function is IrConstructor && function.isPrimary)
+                    ) {
+                        return call
+                    }
+
+                    return irCall(call, getOrCreateStaticMethod(function), dispatchReceiverAsFirstArgument = (function is IrSimpleFunction))
+                }
+
+                override fun visitDelegatingConstructorCall(call: IrDelegatingConstructorCall): IrExpression {
+                    call.transformChildrenVoid(this)
+                    val function = call.symbol.owner
+                    val klass = function.parentAsClass
+                    return when {
+                        !klass.isInline -> call
+                        function.isPrimary -> irCall(call, function)
+                        else -> irCall(call, getOrCreateStaticMethod(function)).apply {
+                            (0 until call.valueArgumentsCount).forEach {
+                                putValueArgument(it, call.getValueArgument(it)!!)
+                            }
+                        }
+                    }
+                }
+
+                private fun getOrCreateStaticMethod(function: IrFunction): IrSimpleFunctionSymbol =
+                    transformedFunction.getOrPut(function.symbol) {
+                        createStaticBodilessMethod(function).also {
+                            function.parentAsClass.declarations.add(it)
+                        }.symbol
+                    }
+            })
+        }
+    }
+
+    private fun Name.toInlineClassImplementationName() = when {
+        isSpecial -> Name.special(asString() + INLINE_CLASS_IMPL_SUFFIX)
+        else -> Name.identifier(asString() + INLINE_CLASS_IMPL_SUFFIX)
+    }
+
+    private fun createStaticBodilessMethod(function: IrFunction): IrSimpleFunction {
+        val descriptor = WrappedSimpleFunctionDescriptor()
+        return IrFunctionImpl(
+            function.startOffset,
+            function.endOffset,
+            function.origin,
+            IrSimpleFunctionSymbolImpl(descriptor),
+            function.name.toInlineClassImplementationName(),
+            function.visibility,
+            Modality.FINAL,
+            function.isInline,
+            function.isExternal,
+            (function is IrSimpleFunction && function.isTailrec),
+            (function is IrSimpleFunction && function.isSuspend)
+        ).apply {
+            descriptor.bind(this)
+            returnType = when (function) {
+                is IrSimpleFunction -> function.returnType
+                is IrConstructor -> function.parentAsClass.defaultType
+                else -> error("Unknown function type")
+            }
+            typeParameters += function.typeParameters
+            annotations += function.annotations
+            dispatchReceiverParameter = null
+            extensionReceiverParameter = function.extensionReceiverParameter?.copyTo(this)
+            if (function is IrSimpleFunction) {
+                valueParameters.add(function.dispatchReceiverParameter!!.copyTo(this, shift = 1))
+                valueParameters += function.valueParameters.map { p -> p.copyTo(this, shift = 1) }
+            } else {
+                valueParameters += function.valueParameters.map { p -> p.copyTo(this, shift = 0) }
+            }
+            parent = function.parent
+            assert(isStaticMethodOfClass)
+        }
+    }
+}
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIntrinsics.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIntrinsics.kt
index d9d2cc411e6..ebce0855f38 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIntrinsics.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIntrinsics.kt
@@ -250,6 +250,9 @@ class JsIntrinsics(private val irBuiltIns: IrBuiltIns, val context: JsIrBackendC
     val jsCharSequenceLength = getInternalFunction("charSequenceLength")
     val jsCharSequenceSubSequence = getInternalFunction("charSequenceSubSequence")
 
+    val jsBoxIntrinsic = getInternalFunction("boxIntrinsic")
+    val jsUnboxIntrinsic = getInternalFunction("unboxIntrinsic")
+
     // Helpers:
 
     private fun getInternalFunction(name: String) =
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/compiler.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/compiler.kt
index abe3f19b91e..3a3532b5cf2 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/compiler.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/compiler.kt
@@ -9,6 +9,7 @@ import com.intellij.openapi.project.Project
 import org.jetbrains.kotlin.backend.common.*
 import org.jetbrains.kotlin.backend.common.extensions.IrGenerationExtension
 import org.jetbrains.kotlin.backend.common.lower.*
+import org.jetbrains.kotlin.backend.common.lower.InlineClassLowering
 import org.jetbrains.kotlin.config.CompilerConfiguration
 import org.jetbrains.kotlin.config.languageVersionSettings
 import org.jetbrains.kotlin.descriptors.ModuleDescriptor
@@ -130,6 +131,11 @@ private fun JsIrBackendContext.lower(moduleFragment: IrModuleFragment, dependenc
         constructorRedirectorLowering.runOnFilesPostfix(moduleFragment)
     }
 
+    InlineClassLowering(this).apply {
+        inlineClassDeclarationLowering.runOnFilesPostfix(moduleFragment)
+        inlineClassUsageLowering.lower(moduleFragment)
+    }
+    AutoboxingTransformer(this).lower(moduleFragment)
 
     ClassReferenceLowering(this).lower(moduleFragment)
     PrimitiveCompanionLowering(this).lower(moduleFragment)
@@ -152,4 +158,4 @@ private fun FunctionLoweringPass.runOnFilesPostfix(moduleFragment: IrModuleFragm
     moduleFragment.files.forEach { runOnFilePostfix(it) }
 
 private fun ClassLoweringPass.runOnFilesPostfix(moduleFragment: IrModuleFragment) =
-    moduleFragment.files.forEach { runOnFilePostfix(it) }
\ No newline at end of file
+    moduleFragment.files.forEach { runOnFilePostfix(it) }
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/AutoboxingTransformer.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/AutoboxingTransformer.kt
new file mode 100644
index 00000000000..ca3e4634623
--- /dev/null
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/AutoboxingTransformer.kt
@@ -0,0 +1,111 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.ir.backend.js.lower
+
+import org.jetbrains.kotlin.backend.common.FileLoweringPass
+import org.jetbrains.kotlin.backend.common.lower.AbstractValueUsageTransformer
+import org.jetbrains.kotlin.ir.backend.js.JsIrBackendContext
+import org.jetbrains.kotlin.ir.backend.js.ir.JsIrBuilder
+import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.expressions.*
+import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.isNothing
+import org.jetbrains.kotlin.ir.types.makeNotNull
+import org.jetbrains.kotlin.ir.util.getInlinedClass
+import org.jetbrains.kotlin.ir.util.isInlined
+
+
+// Copied and adapted from Kotlin/Native
+
+class AutoboxingTransformer(val context: JsIrBackendContext) : AbstractValueUsageTransformer(context.irBuiltIns), FileLoweringPass {
+    override fun lower(irFile: IrFile) {
+        irFile.transformChildrenVoid()
+    }
+
+    override fun IrExpression.useAs(type: IrType): IrExpression {
+
+        val actualType = when (this) {
+            is IrCall -> {
+                if (this.symbol.owner.let { it is IrSimpleFunction && it.isSuspend }) {
+                    irBuiltIns.anyNType
+                } else {
+                    try {
+                        this.symbol.owner.returnType
+                    } catch (e: kotlin.UninitializedPropertyAccessException) {
+                        // TODO: Fix lateinit return types
+                        this.type
+                    }
+                }
+            }
+            is IrGetField -> this.symbol.owner.type
+
+            is IrTypeOperatorCall -> when (this.operator) {
+                IrTypeOperator.IMPLICIT_INTEGER_COERCION ->
+                    // TODO: is it a workaround for inconsistent IR?
+                    this.typeOperand
+
+                IrTypeOperator.CAST, IrTypeOperator.IMPLICIT_CAST -> context.irBuiltIns.anyNType
+
+                else -> this.type
+            }
+
+            is IrGetValue -> {
+                val value = this.symbol.owner
+                if (value is IrValueParameter && value.isDispatchReceiver) {
+                    irBuiltIns.anyNType
+                } else {
+                    this.type
+                }
+            }
+
+            else -> this.type
+        }
+
+        // TODO: Default parameters are passed as nulls and they need not to be unboxed. Fix this
+        if (actualType.makeNotNull().isNothing())
+            return this
+
+        val expectedType = type
+
+        val actualInlinedClass = actualType.getInlinedClass()
+        val expectedInlinedClass = expectedType.getInlinedClass()
+
+        val function = when {
+            actualInlinedClass == null && expectedInlinedClass == null -> return this
+            actualInlinedClass != null && expectedInlinedClass == null -> context.intrinsics.jsBoxIntrinsic
+            actualInlinedClass == null && expectedInlinedClass != null -> context.intrinsics.jsUnboxIntrinsic
+            else -> return this
+        }
+
+        return JsIrBuilder.buildCall(
+            function,
+            expectedType,
+            typeArguments = listOf(actualType, expectedType)
+        ).also {
+            it.putValueArgument(0, this)
+        }
+    }
+
+    override fun IrExpression.useAsVarargElement(expression: IrVararg): IrExpression {
+        return this.useAs(
+            if (this.type.isInlined())
+                irBuiltIns.anyNType
+            else
+                expression.varargElementType
+        )
+    }
+
+    private val IrValueParameter.isDispatchReceiver: Boolean
+        get() {
+            val parent = this.parent
+            if (parent is IrClass)
+                return true
+            if (parent is IrFunction && parent.dispatchReceiverParameter == this)
+                return true
+            return false
+        }
+
+}
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/CallableReferenceLowering.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/CallableReferenceLowering.kt
index bacdf4bc601..83acadcb24f 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/CallableReferenceLowering.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/CallableReferenceLowering.kt
@@ -30,6 +30,7 @@ import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.IrTypeProjection
 import org.jetbrains.kotlin.ir.types.toIrType
+import org.jetbrains.kotlin.ir.util.isInlined
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
 import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
 
@@ -357,6 +358,12 @@ class CallableReferenceLowering(val context: JsIrBackendContext) : FileLoweringP
         return returnStatements
     }
 
+    private fun IrType.boxIfInlined() = if (isInlined()) {
+        context.irBuiltIns.anyNType
+    } else {
+        this
+    }
+
     private fun generateSignatureForClosure(
         callable: IrFunction,
         factory: IrFunction,
@@ -387,7 +394,7 @@ class CallableReferenceLowering(val context: JsIrBackendContext) : FileLoweringP
 
         callable.dispatchReceiverParameter?.let { dispatch ->
             if (reference.dispatchReceiver == null) {
-                result.add(JsIrBuilder.buildValueParameter(dispatch.name, result.size, dispatch.type).also { it.parent = closure })
+                result.add(JsIrBuilder.buildValueParameter(dispatch.name, result.size, dispatch.type.boxIfInlined()).also { it.parent = closure })
             } else {
                 // do not add dispatch receiver in result signature if it is bound
                 capturedParams--
@@ -396,7 +403,7 @@ class CallableReferenceLowering(val context: JsIrBackendContext) : FileLoweringP
 
         callable.extensionReceiverParameter?.let { ext ->
             if (reference.extensionReceiver == null) {
-                result.add(JsIrBuilder.buildValueParameter(ext.name, result.size, ext.type).also { it.parent = closure })
+                result.add(JsIrBuilder.buildValueParameter(ext.name, result.size, ext.type.boxIfInlined()).also { it.parent = closure })
             } else {
                 // the same as for dispatch
                 capturedParams--
@@ -406,7 +413,7 @@ class CallableReferenceLowering(val context: JsIrBackendContext) : FileLoweringP
         for ((index, param) in (result.size until arity).zip(callable.valueParameters.drop(capturedParams))) {
             val type = if (index < functionSignature.size) functionSignature[index] else param.type
             val paramName = param.name.run { if (!isSpecial) identifier else "p$index" }
-            result += JsIrBuilder.buildValueParameter(paramName, result.size, type).also { it.parent = closure }
+            result += JsIrBuilder.buildValueParameter(paramName, result.size, type.boxIfInlined()).also { it.parent = closure }
         }
 
         return result
@@ -492,7 +499,7 @@ class CallableReferenceLowering(val context: JsIrBackendContext) : FileLoweringP
         val boundParamSymbols = factoryFunction.valueParameters.map { it.symbol }
         val unboundParamDeclarations = generateSignatureForClosure(declaration, factoryFunction, closureFunction, reference, arity)
         val unboundParamSymbols = unboundParamDeclarations.map { it.symbol }
-        val returnType = declaration.returnType
+        val returnType = declaration.returnType.boxIfInlined()
 
         closureFunction.valueParameters += unboundParamDeclarations
         closureFunction.returnType = returnType
@@ -540,4 +547,4 @@ class CallableReferenceLowering(val context: JsIrBackendContext) : FileLoweringP
 
         return closureFunction
     }
-}
\ No newline at end of file
+}
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/SecondaryCtorLowering.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/SecondaryCtorLowering.kt
index d191e83163c..ee30515e2bc 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/SecondaryCtorLowering.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/SecondaryCtorLowering.kt
@@ -38,14 +38,18 @@ class SecondaryCtorLowering(val context: JsIrBackendContext) {
 
     val constructorProcessorLowering = object : DeclarationContainerLoweringPass {
         override fun lower(irDeclarationContainer: IrDeclarationContainer) {
-            irDeclarationContainer.declarations.filterIsInstance<IrClass>().forEach { lowerClass(it) }
+            irDeclarationContainer.declarations.filterIsInstance<IrClass>().forEach {
+                if (!it.isInline)  // Inline classes are lowered separately
+                    lowerClass(it)
+            }
         }
     }
 
     val constructorRedirectorLowering = object : DeclarationContainerLoweringPass {
         override fun lower(irDeclarationContainer: IrDeclarationContainer) {
             if (irDeclarationContainer is IrClass) {
-                updateConstructorDeclarations(irDeclarationContainer)
+                if (!irDeclarationContainer.isInline)   // Inline classes are lowered separately
+                    updateConstructorDeclarations(irDeclarationContainer)
             }
             for (it in irDeclarationContainer.declarations) {
                 it.accept(CallsiteRedirectionTransformer(), null)
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/IrElementToJsExpressionTransformer.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/IrElementToJsExpressionTransformer.kt
index 693a479daa7..e98dbf0ae89 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/IrElementToJsExpressionTransformer.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/IrElementToJsExpressionTransformer.kt
@@ -8,12 +8,14 @@ package org.jetbrains.kotlin.ir.backend.js.transformers.irToJs
 import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.ir.backend.js.utils.JsGenerationContext
 import org.jetbrains.kotlin.ir.backend.js.utils.Namer
+import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.symbols.IrConstructorSymbol
 import org.jetbrains.kotlin.ir.types.IrDynamicType
 import org.jetbrains.kotlin.ir.util.isFunctionTypeOrSubtype
+import org.jetbrains.kotlin.ir.util.parentAsClass
 import org.jetbrains.kotlin.js.backend.ast.*
 import org.jetbrains.kotlin.util.OperatorNameConventions
 
@@ -63,6 +65,12 @@ class IrElementToJsExpressionTransformer : BaseIrElementToJsNodeTransformer<JsEx
     }
 
     override fun visitGetField(expression: IrGetField, context: JsGenerationContext): JsExpression {
+        if (expression.symbol.isBound) {
+            val fieldParent = expression.symbol.owner.parent
+            if (fieldParent is IrClass && fieldParent.isInline) {
+                return expression.receiver!!.accept(this, context)
+            }
+        }
         val fieldName = context.getNameForSymbol(expression.symbol)
         return JsNameRef(fieldName, expression.receiver?.accept(this, context))
     }
@@ -100,6 +108,15 @@ class IrElementToJsExpressionTransformer : BaseIrElementToJsNodeTransformer<JsEx
         val thisRef =
             if (fromPrimary) JsThisRef() else context.getNameForSymbol(context.currentFunction!!.valueParameters.last().symbol).makeRef()
         val arguments = translateCallArguments(expression, context)
+
+        val constructor = expression.symbol.owner
+        if (constructor.parentAsClass.isInline) {
+            assert(constructor.isPrimary) {
+                "Delegation to secondary inline constructors must be lowered into simple function calls"
+            }
+            return JsBinaryOperation(JsBinaryOperator.ASG, thisRef, arguments.single())
+        }
+
         return JsInvocation(callFuncRef, listOf(thisRef) + arguments)
     }
 
@@ -127,7 +144,19 @@ class IrElementToJsExpressionTransformer : BaseIrElementToJsNodeTransformer<JsEx
         }
 
         return if (symbol is IrConstructorSymbol) {
-            JsNew(context.getNameForSymbol(symbol).makeRef(), arguments)
+            // Inline class primary constructor takes a single value of to
+            // initialize underlying property.
+            // TODO: Support initialization block
+            val klass = symbol.owner.parentAsClass
+            if (klass.isInline) {
+                assert(symbol.owner.isPrimary) {
+                    "Inline class secondary constructors must be lowered into static methods"
+                }
+                // Argument value constructs unboxed inline class instance
+                arguments.single()
+            } else {
+                JsNew(context.getNameForSymbol(symbol).makeRef(), arguments)
+            }
         } else {
             val symbolName = context.getNameForSymbol(symbol)
             val ref = if (jsDispatchReceiver != null) JsNameRef(symbolName, jsDispatchReceiver) else JsNameRef(symbolName)
@@ -157,4 +186,4 @@ class IrElementToJsExpressionTransformer : BaseIrElementToJsNodeTransformer<JsEx
 
         return simpleFunction.name == OperatorNameConventions.INVOKE && receiverType.isFunctionTypeOrSubtype()
     }
-}
\ No newline at end of file
+}
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/JsIntrinsicTransformers.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/JsIntrinsicTransformers.kt
index 113faf571ca..e8ee061b403 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/JsIntrinsicTransformers.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/JsIntrinsicTransformers.kt
@@ -8,10 +8,13 @@ package org.jetbrains.kotlin.ir.backend.js.transformers.irToJs
 import org.jetbrains.kotlin.ir.backend.js.JsIrBackendContext
 import org.jetbrains.kotlin.ir.backend.js.utils.JsGenerationContext
 import org.jetbrains.kotlin.ir.backend.js.utils.Namer
+import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.declarations.IrFunction
 import org.jetbrains.kotlin.ir.expressions.IrCall
 import org.jetbrains.kotlin.ir.symbols.IrSymbol
 import org.jetbrains.kotlin.ir.types.classifierOrFail
+import org.jetbrains.kotlin.ir.util.getInlineClassBackingField
+import org.jetbrains.kotlin.ir.util.getInlinedClass
 import org.jetbrains.kotlin.js.backend.ast.*
 
 typealias IrCallTransformer = (IrCall, context: JsGenerationContext) -> JsExpression
@@ -183,6 +186,21 @@ class JsIntrinsicTransformers(backendContext: JsIrBackendContext) {
                     JsNew(JsNameRef("${prefix}Array"), translateCallArguments(call, context))
                 }
             }
+
+            add(intrinsics.jsBoxIntrinsic) { call: IrCall, context ->
+                val arg = translateCallArguments(call, context).single()
+                val inlineClass = call.getTypeArgument(0)!!.getInlinedClass()!!
+                val constructor = inlineClass.declarations.filterIsInstance<IrConstructor>().single { it.isPrimary }
+                JsNew(context.getNameForSymbol(constructor.symbol).makeRef(), listOf(arg))
+            }
+
+            add(intrinsics.jsUnboxIntrinsic) { call: IrCall, context ->
+                val arg = translateCallArguments(call, context).single()
+                val inlineClass = call.getTypeArgument(1)!!.getInlinedClass()!!
+                val field = getInlineClassBackingField(inlineClass)
+                val fieldName = context.getNameForSymbol(field.symbol)
+                JsNameRef(fieldName, arg)
+            }
         }
     }
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt
new file mode 100644
index 00000000000..1d199a51fd3
--- /dev/null
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/InlineClasses.kt
@@ -0,0 +1,59 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.ir.util
+
+import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrField
+import org.jetbrains.kotlin.ir.declarations.IrProperty
+import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
+import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
+import org.jetbrains.kotlin.ir.types.IrSimpleType
+import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.classifierOrFail
+import org.jetbrains.kotlin.ir.types.isMarkedNullable
+
+
+/**
+ * Returns inline class for given class or null of type is not inlined
+ * TODO: Make this configurable for different backends (currently implements logic of JS BE)
+ */
+fun IrType.getInlinedClass(): IrClass? {
+    if (this is IrSimpleType) {
+        val erased = erase(this) ?: return null
+        if (!this.isMarkedNullable() && erased.isInline) {
+            // TODO: Don't box nullable type inline classes with non-nullable underlying type (JS IR BE)
+            return erased
+        }
+    }
+    return null
+}
+
+fun IrType.isInlined(): Boolean = this.getInlinedClass() != null
+
+private tailrec fun erase(type: IrType): IrClass? {
+    val classifier = type.classifierOrFail
+
+    // TODO: Fix unbound symbols
+    if (!classifier.isBound)
+        return null
+
+    return when (classifier) {
+        is IrClassSymbol -> classifier.owner
+        is IrTypeParameterSymbol -> erase(classifier.owner.superTypes.first())
+        else -> error(classifier)
+    }
+}
+
+fun getInlineClassBackingField(irClass: IrClass): IrField {
+    for (declaration in irClass.declarations) {
+        if (declaration is IrField)
+            return declaration
+
+        if (declaration is IrProperty)
+            return declaration.backingField ?: continue
+    }
+    error("Inline class has no field")
+}
diff --git a/libraries/stdlib/js/irRuntime/core.kt b/libraries/stdlib/js/irRuntime/core.kt
index 78e15a08609..1c3e85e9402 100644
--- a/libraries/stdlib/js/irRuntime/core.kt
+++ b/libraries/stdlib/js/irRuntime/core.kt
@@ -108,4 +108,7 @@ internal fun newThrowable(message: String?, cause: Throwable?): Throwable {
     throwable.cause = cause
     throwable.name = "Throwable"
     return throwable
-}
\ No newline at end of file
+}
+
+internal fun <T, R> boxIntrinsic(x: T): R = error("Should be lowered")
+internal fun <T, R> unboxIntrinsic(x: T): R = error("Should be lowered")