diff --git a/clox/src/chunk.h b/clox/src/chunk.h
index fe585de..e992c04 100644
--- a/clox/src/chunk.h
+++ b/clox/src/chunk.h
@@ -32,6 +32,7 @@ typedef enum {
   OP_LOOP,
   OP_CALL,
   OP_CLOSURE,
+  OP_CLOSE_UPVALUE,
   OP_RETURN,
 } OpCode;
 
diff --git a/clox/src/compiler.c b/clox/src/compiler.c
index 6e98b5e..75ed697 100644
--- a/clox/src/compiler.c
+++ b/clox/src/compiler.c
@@ -42,6 +42,7 @@ typedef struct {
 typedef struct {
   Token name;
   int depth;
+  bool isCaptured;
 } Local;
 
 typedef struct {
@@ -197,6 +198,7 @@ static void initCompiler(Compiler *compiler, FunctionType type) {
 
   Local *local = &current->locals[current->localCount++];
   local->depth = 0;
+  local->isCaptured = false;
   local->name.start = "";
   local->name.length = 0;
 }
@@ -224,7 +226,11 @@ static void endScope() {
 
   while (current->localCount > 0 &&
          current->locals[current->localCount - 1].depth > current->scopeDepth) {
-    emitByte(OP_POP);
+    if (current->locals[current->localCount - 1].isCaptured) {
+      emitByte(OP_CLOSE_UPVALUE);
+    } else {
+      emitByte(OP_POP);
+    }
     current->localCount--;
   }
 }
@@ -740,6 +746,7 @@ static int resolveUpvalue(Compiler *compiler, Token *name) {
 
   int local = resolveLocal(compiler->enclosing, name);
   if (local != -1) {
+    compiler->enclosing->locals[local].isCaptured = true;
     return addUpvalue(compiler, (uint8_t)local, true);
   }
 
@@ -760,6 +767,7 @@ static void addLocal(Token name) {
   Local *local = &current->locals[current->localCount++];
   local->name = name;
   local->depth = -1;
+  local->isCaptured = false;
 }
 
 static void declareVariable() {
diff --git a/clox/src/debug.c b/clox/src/debug.c
index f175030..750fdb9 100644
--- a/clox/src/debug.c
+++ b/clox/src/debug.c
@@ -118,6 +118,8 @@ int disassembleInstruction(Chunk *chunk, int offset) {
 
     return offset;
   }
+  case OP_CLOSE_UPVALUE:
+    return simpleInstruction("OP_CLOSE_UPVALUE", offset);
   case OP_RETURN:
     return simpleInstruction("OP_RETURN", offset);
   default:
diff --git a/clox/src/memory.c b/clox/src/memory.c
index 3124bb6..1db1c61 100644
--- a/clox/src/memory.c
+++ b/clox/src/memory.c
@@ -18,6 +18,8 @@ void *reallocate(void *pointer, size_t oldSize, size_t newSize) {
 static void freeObject(Obj *object) {
   switch (object->type) {
   case OBJ_CLOSURE: {
+    ObjClosure *closure = (ObjClosure *)object;
+    FREE_ARRAY(ObjUpvalue *, closure->upvalues, closure->upvalueCount);
     FREE(ObjClosure, object);
     break;
   }
@@ -36,6 +38,9 @@ static void freeObject(Obj *object) {
     FREE(ObjString, object);
     break;
   }
+  case OBJ_UPVALUE:
+    FREE(ObjUpvalue, object);
+    break;
   }
 }
 
diff --git a/clox/src/object.c b/clox/src/object.c
index 8d26d8b..31550ae 100644
--- a/clox/src/object.c
+++ b/clox/src/object.c
@@ -20,8 +20,15 @@ static Obj *allocateObject(size_t size, ObjType type) {
 }
 
 ObjClosure *newClosure(ObjFunction *function) {
+  ObjUpvalue **upvalues = ALLOCATE(ObjUpvalue *, function->upvalueCount);
+  for (int i = 0; i < function->upvalueCount; i++) {
+    upvalues[i] = NULL;
+  }
+
   ObjClosure *closure = ALLOCATE_OBJ(ObjClosure, OBJ_CLOSURE);
   closure->function = function;
+  closure->upvalues = upvalues;
+  closure->upvalueCount = function->upvalueCount;
   return closure;
 }
 
@@ -81,6 +88,14 @@ ObjString *copyString(const char *chars, int length) {
   return allocateString(heapChars, length, hash);
 }
 
+ObjUpvalue *newUpvalue(Value *slot) {
+  ObjUpvalue *upvalue = ALLOCATE_OBJ(ObjUpvalue, OBJ_UPVALUE);
+  upvalue->closed = NIL_VAL;
+  upvalue->location = slot;
+  upvalue->next = NULL;
+  return upvalue;
+}
+
 static void printFunction(ObjFunction *function) {
   if (function->name == NULL) {
     printf("<script>");
@@ -103,5 +118,8 @@ void printObject(Value value) {
   case OBJ_STRING:
     printf("%s", AS_CSTRING(value));
     break;
+  case OBJ_UPVALUE:
+    printf("upvalue");
+    break;
   }
 }
diff --git a/clox/src/object.h b/clox/src/object.h
index f650b30..e6b842d 100644
--- a/clox/src/object.h
+++ b/clox/src/object.h
@@ -23,6 +23,7 @@ typedef enum {
   OBJ_FUNCTION,
   OBJ_NATIVE,
   OBJ_STRING,
+  OBJ_UPVALUE,
 } ObjType;
 
 struct Obj {
@@ -52,9 +53,18 @@ struct ObjString {
   uint32_t hash;
 };
 
+typedef struct ObjUpvalue {
+  Obj obj;
+  Value *location;
+  Value closed;
+  struct ObjUpvalue *next;
+} ObjUpvalue;
+
 typedef struct {
   Obj obj;
   ObjFunction *function;
+  ObjUpvalue **upvalues;
+  int upvalueCount;
 } ObjClosure;
 
 ObjClosure *newClosure(ObjFunction *function);
@@ -62,6 +72,7 @@ ObjFunction *newFunction();
 ObjNative *newNative(NativeFn function);
 ObjString *takeString(char *chars, int length);
 ObjString *copyString(const char *chars, int length);
+ObjUpvalue *newUpvalue(Value *slot);
 void printObject(Value value);
 
 static inline bool isObjType(Value value, ObjType type) {
diff --git a/clox/src/vm.c b/clox/src/vm.c
index b728ed5..b11a52a 100644
--- a/clox/src/vm.c
+++ b/clox/src/vm.c
@@ -19,6 +19,7 @@ static Value clockNative(int argCount, Value *args) {
 static void resetStack() {
   vm.stackTop = vm.stack;
   vm.frameCount = 0;
+  vm.openUpvalues = NULL;
 }
 
 static void runtimeError(const char *format, ...) {
@@ -118,6 +119,39 @@ static bool callValue(Value callee, int argCount) {
   return false;
 }
 
+static ObjUpvalue *captureUpvalue(Value *local) {
+  ObjUpvalue *prevUpvalue = NULL;
+  ObjUpvalue *upvalue = vm.openUpvalues;
+  while (upvalue != NULL && upvalue->location > local) {
+    prevUpvalue = upvalue;
+    upvalue = upvalue->next;
+  }
+
+  if (upvalue != NULL && upvalue->location == local) {
+    return upvalue;
+  }
+
+  ObjUpvalue *createdUpvalue = newUpvalue(local);
+  createdUpvalue->next = upvalue;
+
+  if (prevUpvalue == NULL) {
+    vm.openUpvalues = createdUpvalue;
+  } else {
+    prevUpvalue->next = createdUpvalue;
+  }
+
+  return createdUpvalue;
+}
+
+static void closeUpvalues(Value *last) {
+  while (vm.openUpvalues != NULL && vm.openUpvalues->location >= last) {
+    ObjUpvalue *upvalue = vm.openUpvalues;
+    upvalue->closed = *upvalue->location;
+    upvalue->location = &upvalue->closed;
+    vm.openUpvalues = upvalue->next;
+  }
+}
+
 static bool isFalsey(Value value) {
   return IS_NIL(value) || (IS_BOOL(value) && !AS_BOOL(value));
 }
@@ -225,6 +259,16 @@ static InterpretResult run() {
       }
       break;
     }
+    case OP_GET_UPVALUE: {
+      uint8_t slot = READ_BYTE();
+      push(*frame->closure->upvalues[slot]->location);
+      break;
+    }
+    case OP_SET_UPVALUE: {
+      uint8_t slot = READ_BYTE();
+      *frame->closure->upvalues[slot]->location = peek(0);
+      break;
+    }
     case OP_EQUAL: {
       Value b = pop();
       Value a = pop();
@@ -303,10 +347,24 @@ static InterpretResult run() {
       ObjFunction *function = AS_FUNCTION(READ_CONSTANT());
       ObjClosure *closure = newClosure(function);
       push(OBJ_VAL(closure));
+      for (int i = 0; i < closure->upvalueCount; i++) {
+        uint8_t isLocal = READ_BYTE();
+        uint8_t index = READ_BYTE();
+        if (isLocal) {
+          closure->upvalues[i] = captureUpvalue(frame->slots + index);
+        } else {
+          closure->upvalues[i] = frame->closure->upvalues[index];
+        }
+      }
       break;
     }
+    case OP_CLOSE_UPVALUE:
+      closeUpvalues(vm.stackTop - 1);
+      pop();
+      break;
     case OP_RETURN: {
       Value result = pop();
+      closeUpvalues(frame->slots);
       vm.frameCount--;
       if (vm.frameCount == 0) {
         pop();
diff --git a/clox/src/vm.h b/clox/src/vm.h
index ce14d0c..08706a3 100644
--- a/clox/src/vm.h
+++ b/clox/src/vm.h
@@ -23,6 +23,7 @@ typedef struct {
   Value *stackTop;
   Table globals;
   Table strings;
+  ObjUpvalue *openUpvalues;
   Obj *objects;
 } VM;