diff --git a/src/builtins.rs b/src/builtins.rs
index de9060b..c46c9aa 100644
--- a/src/builtins.rs
+++ b/src/builtins.rs
@@ -79,10 +79,28 @@ pub(crate) fn print(vm: &mut Vm, state: FunctionState) -> FunctionResult {
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-// Base function implementations
+// BaseObjInst implementations
 ////////////////////////////////////////////////////////////////////////////////
 
 impl BaseObjInst {
+    //
+    // Common functions
+    //
+
+    pub(crate) fn to_repr(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let str_value = format!("{}", vm.frame_stack()[0].borrow());
+        vm.create_str(str_value).into()
+    }
+
+    pub(crate) fn to_bool(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        vm.create_bool(vm.frame_stack()[0].borrow().is_truthy())
+            .into()
+    }
+
+    //
+    // Operators
+    //
+
     pub(crate) fn and(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
         let lhs = vm.frame_stack()[0].borrow();
         let rhs = vm.frame_stack()[1].borrow();
@@ -149,15 +167,9 @@ impl BaseObjInst {
         }
     }
 
-    pub(crate) fn to_repr(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
-        let str_value = format!("{}", vm.frame_stack()[0].borrow());
-        vm.create_str(str_value).into()
-    }
-
-    pub(crate) fn to_bool(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
-        vm.create_bool(vm.frame_stack()[0].borrow().is_truthy())
-            .into()
-    }
+    //
+    // Not implemented
+    //
 
     pub(crate) fn not_implemented_un(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
         let fname = &vm.frame().name;
@@ -175,5 +187,60 @@ impl BaseObjInst {
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-//
+// StringInst implementations
 ////////////////////////////////////////////////////////////////////////////////
+impl StrInst {
+    pub(crate) fn to_str(_vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        // top item of the stack should just be ourselves, so return immediately
+        FunctionResult::Return
+    }
+
+    pub(crate) fn to_repr(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let escaped: String =
+            with_obj_downcast(vm.frame_stack()[0].clone(), |str_inst: &StrInst| {
+                str_inst.str_value().as_str().escape_default().collect()
+            });
+        vm.create_str(escaped).into()
+    }
+
+    pub(crate) fn len(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let len = with_obj_downcast(vm.frame_stack()[0].clone(), |str_inst: &StrInst| {
+            str_inst.str_value().len() as i64
+        });
+        vm.create_int(len).into()
+    }
+
+    pub(crate) fn add(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let lhs = vm.frame_stack()[0].clone();
+        let rhs = vm.frame_stack()[1].clone();
+        if !obj_is_inst::<StrInst>(&rhs) {
+            // TODO StrInst::add - throw an exception when the RHS is not a string
+            // BLOCKED-ON: exceptions
+            todo!(
+                "can only concatenate Str, got {} instead",
+                rhs.borrow().type_name()
+            )
+        }
+
+        let new = format!("{}{}", lhs.borrow(), rhs.borrow());
+        vm.create_str(new).into()
+    }
+
+    pub(crate) fn mul(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let lhs = vm.frame_stack()[0].clone();
+        let rhs = vm.frame_stack()[1].clone();
+        let repeat_count = if let Some(int_inst) = rhs.borrow().as_any().downcast_ref::<IntInst>() {
+            int_inst.int_value()
+        } else {
+            // TODO StrInst::mul - throw an exception when the RHS is not an int
+            // BLOCKED-ON: exceptions
+            todo!(
+                "can only repeat Str with Int, got {} instead",
+                rhs.borrow().type_name()
+            )
+        };
+        let repeat_count = repeat_count.max(0) as usize;
+        let new = format!("{}", lhs.borrow()).repeat(repeat_count);
+        vm.create_str(new).into()
+    }
+}
diff --git a/src/obj.rs b/src/obj.rs
index 7fea000..70ad0e9 100644
--- a/src/obj.rs
+++ b/src/obj.rs
@@ -116,9 +116,10 @@ pub fn init_types(builtins: &mut HashMap<String, ObjP>) {
         // type definitions
         Type {
             // Method conversion
-            to_string => builtins.create_builtin_function("to_string", BaseObjInst::to_repr, 1),
+            to_str => builtins.create_builtin_function("to_str", BaseObjInst::to_repr, 1),
             to_repr => builtins.create_builtin_function("to_repr", BaseObjInst::to_repr, 1),
             to_bool => builtins.create_builtin_function("to_bool", BaseObjInst::to_bool, 1),
+            len => builtins.create_builtin_function("len", BaseObjInst::not_implemented_un, 1),
             // Operators
             __add__ => builtins.create_builtin_function("__add__", BaseObjInst::not_implemented_bin, 2),
             __sub__ => builtins.create_builtin_function("__sub__", BaseObjInst::not_implemented_bin, 2),
@@ -137,7 +138,14 @@ pub fn init_types(builtins: &mut HashMap<String, ObjP>) {
             __not__ => builtins.create_builtin_function("__not__", BaseObjInst::not, 1),
         },
         Obj { },
-        Str { },
+        Str {
+            to_str => builtins.create_builtin_function("to_str", StrInst::to_str, 1),
+            to_repr => builtins.create_builtin_function("to_repr", StrInst::to_repr, 1),
+            len => builtins.create_builtin_function("len", StrInst::len, 1),
+            // Operators
+            __add__ => builtins.create_builtin_function("__add__", StrInst::add, 2),
+            __mul__ => builtins.create_builtin_function("__mul__", StrInst::mul, 2),
+        },
         Int { },
         Float { },
         Bool { },
@@ -824,7 +832,7 @@ fn test_obj_vtable() {
     let to_string_ptr = str1.borrow_mut().get_attr_lazy(
         str1.clone(),
         builtins.get("Method").unwrap().clone(),
-        "to_string",
+        "to_str",
     );
     assert!(to_string_ptr.is_some());
 
@@ -838,7 +846,7 @@ fn test_obj_vtable() {
     let method_to_string_ptr = to_string_ptr.borrow_mut().get_attr_lazy(
         to_string_ptr.clone(),
         builtins.get("Method").unwrap().clone(),
-        "to_string",
+        "to_str",
     );
     assert!(method_to_string_ptr.is_some());