diff --git a/CHANGELOG.md b/CHANGELOG.md
index e7f76a9797f..62d96498441 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added ProxyTracerProvider and ProxyTracer implementations to allow fetching provider
   and tracer instances before a global provider is set up.
   ([#1726](https://github.com/open-telemetry/opentelemetry-python/pull/1726))
+- Added `__contains__` to `opentelementry.trace.span.TraceState`.
+  ([#1773](https://github.com/open-telemetry/opentelemetry-python/pull/1773))
 
 
 ## [1.0.0](https://github.com/open-telemetry/opentelemetry-python/releases/tag/v1.0.0) - 2021-03-26
diff --git a/opentelemetry-api/src/opentelemetry/trace/span.py b/opentelemetry-api/src/opentelemetry/trace/span.py
index d04cdfa49dd..c4c713cf3e7 100644
--- a/opentelemetry-api/src/opentelemetry/trace/span.py
+++ b/opentelemetry-api/src/opentelemetry/trace/span.py
@@ -231,8 +231,11 @@ def __init__(
                     "Invalid key/value pair (%s, %s) found.", key, value
                 )
 
-    def __getitem__(self, key: str) -> typing.Optional[str]:  # type: ignore
-        return self._dict.get(key)
+    def __contains__(self, item: object) -> bool:
+        return item in self._dict
+
+    def __getitem__(self, key: str) -> str:
+        return self._dict[key]
 
     def __iter__(self) -> typing.Iterator[str]:
         return iter(self._dict)
diff --git a/opentelemetry-api/tests/trace/test_tracestate.py b/opentelemetry-api/tests/trace/test_tracestate.py
index 6665dd612dd..625b260d548 100644
--- a/opentelemetry-api/tests/trace/test_tracestate.py
+++ b/opentelemetry-api/tests/trace/test_tracestate.py
@@ -96,3 +96,19 @@ def test_tracestate_order_changed(self):
         foo_place = entries.index(("foo", "bar33"))  # type: ignore
         prev_first_place = entries.index(("1a-2f@foo", "bar1"))  # type: ignore
         self.assertLessEqual(foo_place, prev_first_place)
+
+    def test_trace_contains(self):
+        entries = [
+            "1a-2f@foo=bar1",
+            "1a-_*/2b@foo=bar2",
+            "foo=bar3",
+            "foo-_*/bar=bar4",
+        ]
+        header_list = [",".join(entries)]
+        state = TraceState.from_header(header_list)
+
+        self.assertTrue("foo" in state)
+        self.assertFalse("bar" in state)
+        self.assertIsNone(state.get("bar"))
+        with self.assertRaises(KeyError):
+            state["bar"]  # pylint:disable=W0104