diff --git a/src/main/kotlin/lumen/compiler/Compiler.kt b/src/main/kotlin/lumen/compiler/Compiler.kt
new file mode 100644
index 0000000..51fc9bd
--- /dev/null
+++ b/src/main/kotlin/lumen/compiler/Compiler.kt
@@ -0,0 +1,445 @@
+package lumen.compiler
+
+import lumen.CompileError
+import lumen.ast.*
+import lumen.bytecode.Chunk
+import lumen.bytecode.Opcode
+import lumen.runtime.BoolValue
+import lumen.runtime.DoubleValue
+import lumen.runtime.FunctionValue
+import lumen.runtime.IntValue
+import lumen.runtime.StringValue
+
+private enum class FunctionType { Script, Function }
+
+private class Local(val name: String, var depth: Int, var captured: Boolean, val mutable: Boolean)
+
+private class UpvalueDesc(val index: Int, val isLocal: Boolean)
+
+private class FunctionScope(
+    val enclosing: FunctionScope?,
+    val type: FunctionType,
+    val name: String
+) {
+    val chunk = Chunk()
+    val locals = ArrayList<Local>()
+    val upvalues = ArrayList<UpvalueDesc>()
+    var scopeDepth = 0
+    var arity = 0
+
+    init {
+        locals.add(Local("", 0, false, false))
+    }
+}
+
+class Compiler(private val globalMutability: MutableMap<String, Boolean> = mutableMapOf()) {
+    private lateinit var scope: FunctionScope
+    private var currentColumn = 0
+
+    fun compile(program: List<Stmt>, returnLastExpr: Boolean = false): FunctionValue {
+        scope = FunctionScope(null, FunctionType.Script, "script")
+        if (returnLastExpr && program.isNotEmpty() && program.last() is ExprStmt) {
+            for (stmt in program.dropLast(1)) statement(stmt)
+            val tail = program.last() as ExprStmt
+            expression(tail.expr)
+            emit(Opcode.Return, tail.line)
+        } else {
+            for (stmt in program) statement(stmt)
+            emitReturnNil(lastLine(program))
+        }
+        return FunctionValue("script", 0, scope.chunk, scope.upvalues.size)
+    }
+
+    private fun lastLine(program: List<Stmt>): Int = if (program.isEmpty()) 1 else program.last().line
+
+    private fun statement(stmt: Stmt) {
+        currentColumn = stmt.column
+        when (stmt) {
+            is ImportStmt -> {}
+            is LetStmt -> letStatement(stmt)
+            is ExprStmt -> {
+                expression(stmt.expr)
+                emit(Opcode.Pop, stmt.line)
+            }
+            is BlockStmt -> {
+                beginScope()
+                stmt.statements.forEach { statement(it) }
+                endScope(stmt.line)
+            }
+            is IfStmt -> ifStatement(stmt)
+            is WhileStmt -> whileStatement(stmt)
+            is ForStmt -> forStatement(stmt)
+            is ReturnStmt -> returnStatement(stmt)
+            is FunctionStmt -> functionStatement(stmt)
+        }
+    }
+
+    private fun letStatement(stmt: LetStmt) {
+        if (scope.scopeDepth == 0) {
+            expression(stmt.initializer)
+            emit(Opcode.DefineGlobal, stmt.line)
+            emit(nameConstant(stmt.name), stmt.line)
+            globalMutability[stmt.name] = stmt.mutable
+        } else {
+            declareLocal(stmt.name, stmt.mutable, stmt.line)
+            expression(stmt.initializer)
+            markInitialized()
+        }
+    }
+
+    private fun ifStatement(stmt: IfStmt) {
+        expression(stmt.condition)
+        val thenJump = emitJump(Opcode.JumpIfFalse, stmt.line)
+        emit(Opcode.Pop, stmt.line)
+        beginScope()
+        stmt.thenBranch.forEach { statement(it) }
+        endScope(stmt.line)
+        val elseJump = emitJump(Opcode.Jump, stmt.line)
+        patchJump(thenJump)
+        emit(Opcode.Pop, stmt.line)
+        if (stmt.elseBranch != null) {
+            beginScope()
+            stmt.elseBranch.forEach { statement(it) }
+            endScope(stmt.line)
+        }
+        patchJump(elseJump)
+    }
+
+    private fun whileStatement(stmt: WhileStmt) {
+        val loopStart = scope.chunk.code.size
+        expression(stmt.condition)
+        val exitJump = emitJump(Opcode.JumpIfFalse, stmt.line)
+        emit(Opcode.Pop, stmt.line)
+        beginScope()
+        stmt.body.forEach { statement(it) }
+        endScope(stmt.line)
+        emitLoop(loopStart, stmt.line)
+        patchJump(exitJump)
+        emit(Opcode.Pop, stmt.line)
+    }
+
+    private fun forStatement(stmt: ForStmt) {
+        beginScope()
+        expression(stmt.iterable)
+        emit(Opcode.GetIter, stmt.line)
+        val iterSlot = addSyntheticLocal("\$iter")
+        emit(Opcode.Nil, stmt.line)
+        val varSlot = declareLocal(stmt.name, true, stmt.line)
+        markInitialized()
+
+        val loopStart = scope.chunk.code.size
+        emit(Opcode.ForIter, stmt.line)
+        emit(iterSlot, stmt.line)
+        val exitPatch = emit(0, stmt.line)
+        emit(Opcode.SetLocal, stmt.line)
+        emit(varSlot, stmt.line)
+        emit(Opcode.Pop, stmt.line)
+
+        beginScope()
+        stmt.body.forEach { statement(it) }
+        endScope(stmt.line)
+
+        emitLoop(loopStart, stmt.line)
+        patchJump(exitPatch)
+        endScope(stmt.line)
+    }
+
+    private fun returnStatement(stmt: ReturnStmt) {
+        if (scope.type == FunctionType.Script) {
+            throw CompileError("'return' outside of a function", stmt.line)
+        }
+        if (stmt.value == null) {
+            emitReturnNil(stmt.line)
+        } else {
+            expression(stmt.value)
+            emit(Opcode.Return, stmt.line)
+        }
+    }
+
+    private fun functionStatement(stmt: FunctionStmt) {
+        if (scope.scopeDepth == 0) {
+            compileFunction(stmt.function)
+            emit(Opcode.DefineGlobal, stmt.line)
+            emit(nameConstant(stmt.name), stmt.line)
+            globalMutability[stmt.name] = true
+        } else {
+            declareLocal(stmt.name, true, stmt.line)
+            markInitialized()
+            compileFunction(stmt.function)
+        }
+    }
+
+    private fun expression(expr: Expr) {
+        currentColumn = expr.column
+        when (expr) {
+            is IntLiteral -> emitConstant(IntValue(expr.value), expr.line)
+            is DoubleLiteral -> emitConstant(DoubleValue(expr.value), expr.line)
+            is StringLiteral -> emitConstant(StringValue(expr.value), expr.line)
+            is BoolLiteral -> emit(if (expr.value) Opcode.True else Opcode.False, expr.line)
+            is NilLiteral -> emit(Opcode.Nil, expr.line)
+            is ListLiteral -> {
+                expr.elements.forEach { expression(it) }
+                emit(Opcode.BuildList, expr.line)
+                emit(expr.elements.size, expr.line)
+            }
+            is MapLiteral -> {
+                expr.entries.forEach { (key, value) ->
+                    expression(key)
+                    expression(value)
+                }
+                emit(Opcode.BuildMap, expr.line)
+                emit(expr.entries.size, expr.line)
+            }
+            is Variable -> variableAccess(expr.name, expr.line)
+            is Assign -> assignment(expr)
+            is Index -> {
+                expression(expr.target)
+                expression(expr.index)
+                emit(Opcode.IndexGet, expr.line)
+            }
+            is IndexAssign -> {
+                expression(expr.target)
+                expression(expr.index)
+                expression(expr.value)
+                emit(Opcode.IndexSet, expr.line)
+            }
+            is Unary -> {
+                expression(expr.operand)
+                emit(if (expr.op == UnaryOp.Negate) Opcode.Negate else Opcode.Not, expr.line)
+            }
+            is Binary -> {
+                expression(expr.left)
+                expression(expr.right)
+                emitBinary(expr.op, expr.line)
+            }
+            is Logical -> logical(expr)
+            is Call -> {
+                expression(expr.callee)
+                expr.args.forEach { expression(it) }
+                currentColumn = expr.column
+                emit(Opcode.Call, expr.line)
+                emit(expr.args.size, expr.line)
+            }
+            is MethodCall -> {
+                expression(expr.receiver)
+                expr.args.forEach { expression(it) }
+                currentColumn = expr.column
+                emit(Opcode.Invoke, expr.line)
+                emit(nameConstant(expr.method), expr.line)
+                emit(expr.args.size, expr.line)
+            }
+            is FunctionExpr -> compileFunction(expr)
+        }
+    }
+
+    private fun assignment(expr: Assign) {
+        expression(expr.value)
+        val local = resolveLocal(scope, expr.name, expr.line)
+        if (local != -1) {
+            if (!scope.locals[local].mutable) {
+                throw CompileError("cannot assign to immutable '${expr.name}'", expr.line)
+            }
+            emit(Opcode.SetLocal, expr.line)
+            emit(local, expr.line)
+            return
+        }
+        val upvalue = resolveUpvalue(scope, expr.name, expr.line)
+        if (upvalue != -1) {
+            emit(Opcode.SetUpvalue, expr.line)
+            emit(upvalue, expr.line)
+            return
+        }
+        if (globalMutability[expr.name] == false) {
+            throw CompileError("cannot assign to immutable '${expr.name}'", expr.line)
+        }
+        emit(Opcode.SetGlobal, expr.line)
+        emit(nameConstant(expr.name), expr.line)
+    }
+
+    private fun variableAccess(name: String, line: Int) {
+        val local = resolveLocal(scope, name, line)
+        if (local != -1) {
+            emit(Opcode.GetLocal, line)
+            emit(local, line)
+            return
+        }
+        val upvalue = resolveUpvalue(scope, name, line)
+        if (upvalue != -1) {
+            emit(Opcode.GetUpvalue, line)
+            emit(upvalue, line)
+            return
+        }
+        emit(Opcode.GetGlobal, line)
+        emit(nameConstant(name), line)
+    }
+
+    private fun logical(expr: Logical) {
+        when (expr.op) {
+            LogicalOp.And -> {
+                expression(expr.left)
+                val endJump = emitJump(Opcode.JumpIfFalse, expr.line)
+                emit(Opcode.Pop, expr.line)
+                expression(expr.right)
+                patchJump(endJump)
+            }
+            LogicalOp.Or -> {
+                expression(expr.left)
+                val elseJump = emitJump(Opcode.JumpIfFalse, expr.line)
+                val endJump = emitJump(Opcode.Jump, expr.line)
+                patchJump(elseJump)
+                emit(Opcode.Pop, expr.line)
+                expression(expr.right)
+                patchJump(endJump)
+            }
+        }
+    }
+
+    private fun emitBinary(op: BinaryOp, line: Int) {
+        val opcode = when (op) {
+            BinaryOp.Add -> Opcode.Add
+            BinaryOp.Sub -> Opcode.Sub
+            BinaryOp.Mul -> Opcode.Mul
+            BinaryOp.Div -> Opcode.Div
+            BinaryOp.Mod -> Opcode.Mod
+            BinaryOp.Equal -> Opcode.Equal
+            BinaryOp.NotEqual -> Opcode.NotEqual
+            BinaryOp.Less -> Opcode.Less
+            BinaryOp.LessEqual -> Opcode.LessEqual
+            BinaryOp.Greater -> Opcode.Greater
+            BinaryOp.GreaterEqual -> Opcode.GreaterEqual
+        }
+        emit(opcode, line)
+    }
+
+    private fun compileFunction(fnExpr: FunctionExpr) {
+        val enclosing = scope
+        scope = FunctionScope(enclosing, FunctionType.Function, fnExpr.name ?: "anonymous")
+        scope.arity = fnExpr.params.size
+        beginScope()
+        for (param in fnExpr.params) {
+            declareLocal(param, true, fnExpr.line)
+            markInitialized()
+        }
+        fnExpr.body.forEach { statement(it) }
+        emitReturnNil(fnExpr.line)
+
+        val compiled = scope
+        val function = FunctionValue(compiled.name, compiled.arity, compiled.chunk, compiled.upvalues.size)
+        scope = enclosing
+
+        emit(Opcode.Closure, fnExpr.line)
+        emit(addConstant(function), fnExpr.line)
+        for (upvalue in compiled.upvalues) {
+            emit(if (upvalue.isLocal) 1 else 0, fnExpr.line)
+            emit(upvalue.index, fnExpr.line)
+        }
+    }
+
+    private fun beginScope() {
+        scope.scopeDepth++
+    }
+
+    private fun endScope(line: Int) {
+        scope.scopeDepth--
+        while (scope.locals.isNotEmpty() && scope.locals.last().depth > scope.scopeDepth) {
+            if (scope.locals.last().captured) {
+                emit(Opcode.CloseUpvalue, line)
+            } else {
+                emit(Opcode.Pop, line)
+            }
+            scope.locals.removeAt(scope.locals.size - 1)
+        }
+    }
+
+    private fun declareLocal(name: String, mutable: Boolean, line: Int): Int {
+        for (i in scope.locals.indices.reversed()) {
+            val local = scope.locals[i]
+            if (local.depth != -1 && local.depth < scope.scopeDepth) break
+            if (local.name == name) {
+                throw CompileError("'$name' is already declared in this scope", line)
+            }
+        }
+        scope.locals.add(Local(name, -1, false, mutable))
+        return scope.locals.size - 1
+    }
+
+    private fun addSyntheticLocal(name: String): Int {
+        scope.locals.add(Local(name, scope.scopeDepth, false, false))
+        return scope.locals.size - 1
+    }
+
+    private fun markInitialized() {
+        if (scope.scopeDepth == 0) return
+        scope.locals.last().depth = scope.scopeDepth
+    }
+
+    private fun resolveLocal(target: FunctionScope, name: String, line: Int): Int {
+        for (i in target.locals.indices.reversed()) {
+            val local = target.locals[i]
+            if (local.name == name) {
+                if (local.depth == -1) {
+                    throw CompileError("cannot read '$name' in its own initializer", line)
+                }
+                return i
+            }
+        }
+        return -1
+    }
+
+    private fun resolveUpvalue(target: FunctionScope, name: String, line: Int): Int {
+        val enclosing = target.enclosing ?: return -1
+        val local = resolveLocal(enclosing, name, line)
+        if (local != -1) {
+            enclosing.locals[local].captured = true
+            return addUpvalue(target, local, true)
+        }
+        val upvalue = resolveUpvalue(enclosing, name, line)
+        if (upvalue != -1) {
+            return addUpvalue(target, upvalue, false)
+        }
+        return -1
+    }
+
+    private fun addUpvalue(target: FunctionScope, index: Int, isLocal: Boolean): Int {
+        for (i in target.upvalues.indices) {
+            val existing = target.upvalues[i]
+            if (existing.index == index && existing.isLocal == isLocal) return i
+        }
+        target.upvalues.add(UpvalueDesc(index, isLocal))
+        return target.upvalues.size - 1
+    }
+
+    private fun nameConstant(name: String): Int = addConstant(StringValue(name))
+
+    private fun addConstant(value: lumen.runtime.Value): Int = scope.chunk.addConstant(value)
+
+    private fun emitConstant(value: lumen.runtime.Value, line: Int) {
+        emit(Opcode.Constant, line)
+        emit(addConstant(value), line)
+    }
+
+    private fun emit(op: Opcode, line: Int): Int = scope.chunk.emit(op, line, currentColumn)
+
+    private fun emit(byte: Int, line: Int): Int = scope.chunk.emit(byte, line, currentColumn)
+
+    private fun emitReturnNil(line: Int) {
+        emit(Opcode.Nil, line)
+        emit(Opcode.Return, line)
+    }
+
+    private fun emitJump(op: Opcode, line: Int): Int {
+        emit(op, line)
+        return emit(0, line)
+    }
+
+    private fun patchJump(offsetIndex: Int) {
+        val jump = scope.chunk.code.size - (offsetIndex + 1)
+        scope.chunk.patch(offsetIndex, jump)
+    }
+
+    private fun emitLoop(loopStart: Int, line: Int) {
+        emit(Opcode.Loop, line)
+        val offset = scope.chunk.code.size + 1 - loopStart
+        emit(offset, line)
+    }
+}