diff --git a/src/obj/list.rs b/src/obj/list.rs
index 6253cb1..062b13d 100644
--- a/src/obj/list.rs
+++ b/src/obj/list.rs
@@ -185,6 +185,12 @@ impl List {
         FunctionResult::ReturnPush(item)
     }
 
+    pub(crate) fn len(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let this = vm.frame_stack()[0].clone();
+        let len = with_obj_downcast(this, |list: &List| list.list().len());
+        Int::create(len as i64).into()
+    }
+
     pub(crate) fn push(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
         let this = vm.frame_stack()[0].clone();
         let arg = vm.frame_stack()[1].clone();
diff --git a/src/obj/ty.rs b/src/obj/ty.rs
index dc08b5e..7dcba81 100644
--- a/src/obj/ty.rs
+++ b/src/obj/ty.rs
@@ -158,7 +158,6 @@ pub fn init_types() {
             to_int => BuiltinFunction::create("to_int", BaseObj::not_implemented_un, 1),
             to_float => BuiltinFunction::create("to_float", BaseObj::not_implemented_un, 1),
             to_list => BuiltinFunction::create("to_list", BaseObj::not_implemented_un, 1),
-            len => BuiltinFunction::create("len", BaseObj::not_implemented_un, 1),
 
             // Constructor
             // TODO Ty::do_call, Ty::init - implement these methods
@@ -181,6 +180,9 @@ pub fn init_types() {
             __pos__ => BuiltinFunction::create("__pos__", BaseObj::not_implemented_un, 1),
             __neg__ => BuiltinFunction::create("__neg__", BaseObj::not_implemented_un, 1),
             __not__ => BuiltinFunction::create("__not__", BaseObj::not, 1),
+
+            // Methods
+            len => BuiltinFunction::create("len", BaseObj::not_implemented_un, 1),
         },
         Obj {
             //__call__ => BuiltinFunction::create("__call__",
@@ -197,6 +199,8 @@ pub fn init_types() {
             __index__ => BuiltinFunction::create("__index__", List::index, 2),
 
             // Methods
+            len => BuiltinFunction::create("len", List::len, 1),
+
             push => BuiltinFunction::create("push", List::push, 2),
             pop => BuiltinFunction::create("pop", List::pop, 1),
         },
@@ -206,7 +210,6 @@ pub fn init_types() {
             to_int => BuiltinFunction::create("to_int", Str::to_int, 1),
             to_float => BuiltinFunction::create("to_float", Str::to_float, 1),
             to_list => BuiltinFunction::create("to_list", Str::to_list, 1),
-            len => BuiltinFunction::create("len", Str::len, 1),
 
             // Constructor
             __call__ => BuiltinFunction::create("__call__", Str::do_call, 2),
@@ -219,6 +222,7 @@ pub fn init_types() {
             __index__ => BuiltinFunction::create("__index__", Str::index, 2),
 
             // Methods
+            len => BuiltinFunction::create("len", Str::len, 1),
             // TODO Str methods - .lower, .upper, .slice, etc
         },
         Int {