diff --git a/tests/snippets/membership.py b/tests/snippets/membership.py
new file mode 100644
index 000000000..3b76b8052
--- /dev/null
+++ b/tests/snippets/membership.py
@@ -0,0 +1,62 @@
+# test lists
+assert 3 in [1, 2, 3]
+assert 3 not in [1, 2]
+
+assert not (3 in [1, 2])
+assert not (3 not in [1, 2, 3])
+
+# test strings
+assert "foo" in "foobar"
+assert "whatever" not in "foobar"
+
+# test bytes
+# TODO: uncomment this when bytes are implemented
+# assert b"foo" in b"foobar"
+# assert b"whatever" not in b"foobar"
+
+# test tuple
+assert 1 in (1, 2)
+assert 3 not in (1, 2)
+
+# test set
+# TODO: uncomment this when sets are implemented
+# assert 1 in set(1, 2)
+# assert 3 not in set(1, 2)
+
+# test dicts
+# TODO: test dicts when keys other than strings will be allowed
+assert "a" in {"a": 0, "b": 0}
+assert "c" not in {"a": 0, "b": 0}
+
+# test iter
+assert 3 in iter([1, 2, 3])
+assert 3 not in iter([1, 2])
+
+# test sequence
+# TODO: uncomment this when ranges are usable
+# assert 1 in range(0, 2)
+# assert 3 not in range(0, 2)
+
+# test __contains__ in user objects
+class MyNotContainingClass():
+    pass
+
+
+try:
+    1 in MyNotContainingClass()
+except TypeError:
+    pass
+else:
+    assert False, "TypeError not raised"
+
+
+class MyContainingClass():
+    def __init__(self, value):
+        self.value = value
+
+    def __contains__(self, something):
+        return something == self.value
+
+
+assert 2 in MyContainingClass(2)
+assert 1 not in MyContainingClass(2)
diff --git a/vm/src/obj/objdict.rs b/vm/src/obj/objdict.rs
index 6729278a5..910105b57 100644
--- a/vm/src/obj/objdict.rs
+++ b/vm/src/obj/objdict.rs
@@ -63,6 +63,26 @@ fn dict_repr(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
     Ok(vm.new_str(s))
 }
 
+pub fn dict_contains(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
+    arg_check!(
+        vm,
+        args,
+        required = [
+            (dict, Some(vm.ctx.dict_type())),
+            (needle, Some(vm.ctx.str_type()))
+        ]
+    );
+
+    let needle = objstr::get_value(&needle);
+    for element in get_elements(dict).iter() {
+        if &needle == element.0 {
+            return Ok(vm.new_bool(true));
+        }
+    }
+
+    Ok(vm.new_bool(false))
+}
+
 pub fn create_type(type_type: PyObjectRef, object_type: PyObjectRef, dict_type: PyObjectRef) {
     (*dict_type.borrow_mut()).kind = PyObjectKind::Class {
         name: String::from("dict"),
@@ -75,6 +95,7 @@ pub fn create_type(type_type: PyObjectRef, object_type: PyObjectRef, dict_type:
 pub fn init(context: &PyContext) {
     let ref dict_type = context.dict_type;
     dict_type.set_attr("__len__", context.new_rustfunc(dict_len));
+    dict_type.set_attr("__contains__", context.new_rustfunc(dict_contains));
     dict_type.set_attr("__new__", context.new_rustfunc(dict_new));
     dict_type.set_attr("__repr__", context.new_rustfunc(dict_repr));
 }
diff --git a/vm/src/obj/objiter.rs b/vm/src/obj/objiter.rs
index 09afd8ce3..90fff2d1d 100644
--- a/vm/src/obj/objiter.rs
+++ b/vm/src/obj/objiter.rs
@@ -53,6 +53,26 @@ fn iter_iter(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
     Ok(iter.clone())
 }
 
+fn iter_contains(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
+    arg_check!(
+        vm,
+        args,
+        required = [(iter, Some(vm.ctx.iter_type())), (needle, None)]
+    );
+    loop {
+        match vm.call_method(&iter, "__next__", vec![]) {
+            Ok(element) => {
+                if &element == needle {
+                    return Ok(vm.new_bool(true));
+                } else {
+                    continue;
+                }
+            }
+            Err(_) => return Ok(vm.new_bool(false)),
+        }
+    }
+}
+
 fn iter_next(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
     arg_check!(vm, args, required = [(iter, Some(vm.ctx.iter_type()))]);
 
@@ -86,7 +106,8 @@ fn iter_next(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
 
 pub fn init(context: &PyContext) {
     let ref iter_type = context.iter_type;
-    iter_type.set_attr("__new__", context.new_rustfunc(iter_new));
+    iter_type.set_attr("__contains__", context.new_rustfunc(iter_contains));
     iter_type.set_attr("__iter__", context.new_rustfunc(iter_iter));
+    iter_type.set_attr("__new__", context.new_rustfunc(iter_new));
     iter_type.set_attr("__next__", context.new_rustfunc(iter_next));
 }
diff --git a/vm/src/obj/objlist.rs b/vm/src/obj/objlist.rs
index 605bfdc4a..24831e452 100644
--- a/vm/src/obj/objlist.rs
+++ b/vm/src/obj/objlist.rs
@@ -162,10 +162,27 @@ fn reverse(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
     }
 }
 
+pub fn contains(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
+    trace!("list.len called with: {:?}", args);
+    arg_check!(
+        vm,
+        args,
+        required = [(list, Some(vm.ctx.list_type())), (x, None)]
+    );
+    for element in get_elements(list).iter() {
+        if x == element {
+            return Ok(vm.new_bool(true));
+        }
+    }
+
+    Ok(vm.new_bool(false))
+}
+
 pub fn init(context: &PyContext) {
     let ref list_type = context.list_type;
-    list_type.set_attr("__eq__", context.new_rustfunc(list_eq));
     list_type.set_attr("__add__", context.new_rustfunc(list_add));
+    list_type.set_attr("__contains__", context.new_rustfunc(contains));
+    list_type.set_attr("__eq__", context.new_rustfunc(list_eq));
     list_type.set_attr("__len__", context.new_rustfunc(list_len));
     list_type.set_attr("__new__", context.new_rustfunc(list_new));
     list_type.set_attr("__repr__", context.new_rustfunc(list_repr));
diff --git a/vm/src/obj/objstr.rs b/vm/src/obj/objstr.rs
index 5725e5b4d..009a0d9c5 100644
--- a/vm/src/obj/objstr.rs
+++ b/vm/src/obj/objstr.rs
@@ -8,8 +8,9 @@ use super::objtype;
 
 pub fn init(context: &PyContext) {
     let ref str_type = context.str_type;
-    str_type.set_attr("__eq__", context.new_rustfunc(str_eq));
     str_type.set_attr("__add__", context.new_rustfunc(str_add));
+    str_type.set_attr("__eq__", context.new_rustfunc(str_eq));
+    str_type.set_attr("__contains__", context.new_rustfunc(str_contains));
     str_type.set_attr("__len__", context.new_rustfunc(str_len));
     str_type.set_attr("__mul__", context.new_rustfunc(str_mul));
     str_type.set_attr("__new__", context.new_rustfunc(str_new));
@@ -197,6 +198,20 @@ fn str_startswith(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
     Ok(vm.ctx.new_bool(value.starts_with(pat.as_str())))
 }
 
+fn str_contains(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
+    arg_check!(
+        vm,
+        args,
+        required = [
+            (s, Some(vm.ctx.str_type())),
+            (needle, Some(vm.ctx.str_type()))
+        ]
+    );
+    let value = get_value(&s);
+    let needle = get_value(&needle);
+    Ok(vm.ctx.new_bool(value.contains(needle.as_str())))
+}
+
 // TODO: should with following format
 // class str(object='')
 // class str(object=b'', encoding='utf-8', errors='strict')
diff --git a/vm/src/obj/objtuple.rs b/vm/src/obj/objtuple.rs
index 3643f4f52..adb4e8d47 100644
--- a/vm/src/obj/objtuple.rs
+++ b/vm/src/obj/objtuple.rs
@@ -50,6 +50,21 @@ fn tuple_repr(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
     Ok(vm.new_str(s))
 }
 
+pub fn tuple_contains(vm: &mut VirtualMachine, args: PyFuncArgs) -> PyResult {
+    arg_check!(
+        vm,
+        args,
+        required = [(tuple, Some(vm.ctx.tuple_type())), (x, None)]
+    );
+    for element in get_elements(tuple).iter() {
+        if x == element {
+            return Ok(vm.new_bool(true));
+        }
+    }
+
+    Ok(vm.new_bool(false))
+}
+
 pub fn get_elements(obj: &PyObjectRef) -> Vec<PyObjectRef> {
     if let PyObjectKind::Tuple { elements } = &obj.borrow().kind {
         elements.to_vec()
@@ -61,6 +76,7 @@ pub fn get_elements(obj: &PyObjectRef) -> Vec<PyObjectRef> {
 pub fn init(context: &PyContext) {
     let ref tuple_type = context.tuple_type;
     tuple_type.set_attr("__eq__", context.new_rustfunc(tuple_eq));
+    tuple_type.set_attr("__contains__", context.new_rustfunc(tuple_contains));
     tuple_type.set_attr("__len__", context.new_rustfunc(tuple_len));
     tuple_type.set_attr("__repr__", context.new_rustfunc(tuple_repr));
 }
diff --git a/vm/src/vm.rs b/vm/src/vm.rs
index af2b3677a..4ef7bddcc 100644
--- a/vm/src/vm.rs
+++ b/vm/src/vm.rs
@@ -580,6 +580,33 @@ impl VirtualMachine {
         a.get_id()
     }
 
+    // https://docs.python.org/3/reference/expressions.html#membership-test-operations
+    fn _membership(&mut self, needle: PyObjectRef, haystack: &PyObjectRef) -> PyResult {
+        self.call_method(&haystack, "__contains__", vec![needle])
+        // TODO: implement __iter__ and __getitem__ cases when __contains__ is
+        // not implemented.
+    }
+
+    fn _in(&mut self, needle: PyObjectRef, haystack: PyObjectRef) -> PyResult {
+        match self._membership(needle, &haystack) {
+            Ok(found) => Ok(found),
+            Err(_) => Err(self.new_type_error(format!(
+                "{} has no __contains__ method",
+                objtype::get_type_name(&haystack.typ())
+            ))),
+        }
+    }
+
+    fn _not_in(&mut self, needle: PyObjectRef, haystack: PyObjectRef) -> PyResult {
+        match self._membership(needle, &haystack) {
+            Ok(found) => Ok(self.ctx.new_bool(!objbool::get_value(&found))),
+            Err(_) => Err(self.new_type_error(format!(
+                "{} has no __contains__ method",
+                objtype::get_type_name(&haystack.typ())
+            ))),
+        }
+    }
+
     fn _is(&self, a: PyObjectRef, b: PyObjectRef) -> bool {
         // Pointer equal:
         a.is(&b)
@@ -603,7 +630,8 @@ impl VirtualMachine {
             &bytecode::ComparisonOperator::GreaterOrEqual => self._ge(a, b),
             &bytecode::ComparisonOperator::Is => Ok(self.ctx.new_bool(self._is(a, b))),
             &bytecode::ComparisonOperator::IsNot => self._is_not(a, b),
-            _ => panic!("NOT IMPL {:?}", op),
+            &bytecode::ComparisonOperator::In => self._in(a, b),
+            &bytecode::ComparisonOperator::NotIn => self._not_in(a, b),
         };
         match result {
             Ok(value) => {