diff --git a/src/obj/list.rs b/src/obj/list.rs
index 062b13d..1f0ce5d 100644
--- a/src/obj/list.rs
+++ b/src/obj/list.rs
@@ -125,7 +125,7 @@ impl List {
                 if index == this.list().len() {
                     // if this is the last item in the list, then we're done
                     let new_str = format!("{}{}]", build_str.borrow(), repr_str.borrow());
-                    FunctionResult::ReturnPush(Str::create(new_str))
+                    Str::create(new_str).into()
                 } else {
                     // otherwise, continue building the string and calling to_repr
                     let new_str = format!("{}{}, ", build_str.borrow(), repr_str.borrow());
@@ -145,6 +145,13 @@ impl List {
         }
     }
 
+    pub(crate) fn to_list(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        // create a clone of this list
+        let this = vm.frame_stack()[0].clone();
+        let list_items = with_obj_downcast(this, |list: &List| list.list().clone());
+        List::create(list_items).into()
+    }
+
     impl_do_call!(to_list);
 
     pub(crate) fn init(_vm: &mut Vm, _state: FunctionState) -> FunctionResult {
@@ -182,7 +189,7 @@ impl List {
             }
         });
 
-        FunctionResult::ReturnPush(item)
+        item.into()
     }
 
     pub(crate) fn len(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
@@ -195,7 +202,7 @@ impl List {
         let this = vm.frame_stack()[0].clone();
         let arg = vm.frame_stack()[1].clone();
         with_obj_downcast_mut(this, |list: &mut List| list.list_mut().push(arg));
-        FunctionResult::ReturnPush(Nil::create())
+        Nil::create().into()
     }
 
     pub(crate) fn pop(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
@@ -210,6 +217,27 @@ impl List {
             todo!("throw an exception when the list is empty and there is nothing to pop")
         };
 
-        FunctionResult::ReturnPush(last)
+        last.into()
+    }
+
+    pub(crate) fn extend(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let this = vm.frame_stack()[0].clone();
+        let arg = vm.frame_stack()[1].clone();
+
+        // we have to clone here, in case this and arg are the same list. otherwise, we couldn't
+        // borrow `this` mutably while using `list` immutably.
+        let list_extension = if let Some(list) = arg.borrow().as_any().downcast_ref::<List>() {
+            list.list().clone()
+        } else {
+            // TODO List::extend - throw an exception when the argument is not a list
+            // BLOCKED-ON: exceptions
+            todo!("throw an exception when the List.extend argument is not a list")
+        };
+
+        with_obj_downcast_mut(this, |list: &mut List| {
+            list.list_mut().extend(list_extension);
+        });
+
+        Nil::create().into()
     }
 }
diff --git a/src/obj/ty.rs b/src/obj/ty.rs
index 7dcba81..eecade5 100644
--- a/src/obj/ty.rs
+++ b/src/obj/ty.rs
@@ -190,6 +190,7 @@ pub fn init_types() {
         List {
             // Conversion methods
             to_repr => BuiltinFunction::create("to_repr", List::to_repr, 1),
+            to_list => BuiltinFunction::create("to_list", List::to_list, 1),
 
             // Constructor
             __call__ => BuiltinFunction::create("__call__", List::do_call, 2),
@@ -203,6 +204,7 @@ pub fn init_types() {
 
             push => BuiltinFunction::create("push", List::push, 2),
             pop => BuiltinFunction::create("pop", List::pop, 1),
+            extend => BuiltinFunction::create("extend", List::extend, 2),
         },
         Str {
             // Conversion methods
diff --git a/tests/list.npp b/tests/list.npp
new file mode 100644
index 0000000..b4ebae4
--- /dev/null
+++ b/tests/list.npp
@@ -0,0 +1,51 @@
+# List type operator and function tests
+
+a = []
+
+println("to_str")
+println(a.to_str())
+println([1, 2, 3])
+println(["a", "b", "c"])
+println(["a\nb\nc"])
+
+println("push and pop")
+a.push(1234)
+a.push(56)
+println(a)
+println(a.pop())
+println(a)
+a.push(99)
+a.push(100)
+println(a)
+a.pop()
+a.pop()
+a.push('99')
+a.push('100')
+println(a)
+
+println("len")
+println(a.len())
+a.pop()
+println(a.len())
+a.pop()
+println(a.len())
+a.pop()
+println(a.len())
+
+println("extend")
+a.extend([1, 2, 3])
+println(a)
+a.extend([1, 2, 3])
+println(a)
+a.extend(['a', 's', 'd', 'f'])
+println(a)
+
+println("constructor")
+println(List("asdf"))
+println(List([1, 2, 3]))
+# ensure that creating a new list actually clones it
+b = [1, 2, 3]
+c = List(b)
+c.pop()
+println(b)
+println(c)
diff --git a/tests/list.npp.expect b/tests/list.npp.expect
new file mode 100644
index 0000000..e6e0f12
--- /dev/null
+++ b/tests/list.npp.expect
@@ -0,0 +1,25 @@
+to_str
+[]
+[1, 2, 3]
+['a', 'b', 'c']
+['a\nb\nc']
+push and pop
+[1234, 56]
+56
+[1234]
+[1234, 99, 100]
+[1234, '99', '100']
+len
+3
+2
+1
+0
+extend
+[1, 2, 3]
+[1, 2, 3, 1, 2, 3]
+[1, 2, 3, 1, 2, 3, 'a', 's', 'd', 'f']
+constructor
+['a', 's', 'd', 'f']
+[1, 2, 3]
+[1, 2, 3]
+[1, 2]