diff --git a/google/cloud/firestore_v1/base_query.py b/google/cloud/firestore_v1/base_query.py
index 188c15b6a..38d08dd14 100644
--- a/google/cloud/firestore_v1/base_query.py
+++ b/google/cloud/firestore_v1/base_query.py
@@ -56,10 +56,12 @@
     "<": _operator_enum.LESS_THAN,
     "<=": _operator_enum.LESS_THAN_OR_EQUAL,
     _EQ_OP: _operator_enum.EQUAL,
+    "!=": _operator_enum.NOT_EQUAL,
     ">=": _operator_enum.GREATER_THAN_OR_EQUAL,
     ">": _operator_enum.GREATER_THAN,
     "array_contains": _operator_enum.ARRAY_CONTAINS,
     "in": _operator_enum.IN,
+    "not-in": _operator_enum.NOT_IN,
     "array_contains_any": _operator_enum.ARRAY_CONTAINS_ANY,
 }
 _BAD_OP_STRING = "Operator string {!r} is invalid. Valid choices are: {}."
@@ -255,8 +257,8 @@ def where(self, field_path: str, op_string: str, value) -> "BaseQuery":
             field_path (str): A field path (``.``-delimited list of
                 field names) for the field to filter on.
             op_string (str): A comparison operation in the form of a string.
-                Acceptable values are ``<``, ``<=``, ``==``, ``>=``, ``>``,
-                ``in``, ``array_contains`` and ``array_contains_any``.
+                Acceptable values are ``<``, ``<=``, ``==``, ``!=``, ``>=``, ``>``,
+                ``in``, ``not-in``, ``array_contains`` and ``array_contains_any``.
             value (Any): The value to compare the field against in the filter.
                 If ``value`` is :data:`None` or a NaN, then ``==`` is the only
                 allowed operation.
@@ -864,7 +866,7 @@ def _enum_from_op_string(op_string: str) -> Any:
 
     Args:
         op_string (str): A comparison operation in the form of a string.
-            Acceptable values are ``<``, ``<=``, ``==``, ``>=``
+            Acceptable values are ``<``, ``<=``, ``==``, ``!=``, ``>=``
             and ``>``.
 
     Returns:
diff --git a/tests/system/test_system.py b/tests/system/test_system.py
index 988fa082c..355c5aebb 100644
--- a/tests/system/test_system.py
+++ b/tests/system/test_system.py
@@ -582,6 +582,36 @@ def test_query_stream_w_simple_field_in_op(query_docs):
         assert value["a"] == 1
 
 
+def test_query_stream_w_not_eq_op(query_docs):
+    collection, stored, allowed_vals = query_docs
+    query = collection.where("stats.sum", "!=", 4)
+    values = {snapshot.id: snapshot.to_dict() for snapshot in query.stream()}
+    assert len(values) == 20
+    ab_pairs2 = set()
+    for key, value in values.items():
+        assert stored[key] == value
+        ab_pairs2.add((value["a"], value["b"]))
+
+    expected_ab_pairs = set(
+        [
+            (a_val, b_val)
+            for a_val in allowed_vals
+            for b_val in allowed_vals
+            if a_val + b_val != 4
+        ]
+    )
+    assert expected_ab_pairs == ab_pairs2
+
+
+def test_query_stream_w_simple_not_in_op(query_docs):
+    collection, stored, allowed_vals = query_docs
+    num_vals = len(allowed_vals)
+    query = collection.where("stats.sum", "not-in", [2, num_vals + 100])
+    values = {snapshot.id: snapshot.to_dict() for snapshot in query.stream()}
+
+    assert len(values) == 22
+
+
 def test_query_stream_w_simple_field_array_contains_any_op(query_docs):
     collection, stored, allowed_vals = query_docs
     num_vals = len(allowed_vals)
diff --git a/tests/unit/v1/test_base_query.py b/tests/unit/v1/test_base_query.py
index 59578af39..4b22f6cd8 100644
--- a/tests/unit/v1/test_base_query.py
+++ b/tests/unit/v1/test_base_query.py
@@ -1186,6 +1186,14 @@ def test_array_contains_any(self):
             self._call_fut("array_contains_any"), op_class.ARRAY_CONTAINS_ANY
         )
 
+    def test_not_in(self):
+        op_class = self._get_op_class()
+        self.assertEqual(self._call_fut("not-in"), op_class.NOT_IN)
+
+    def test_not_eq(self):
+        op_class = self._get_op_class()
+        self.assertEqual(self._call_fut("!="), op_class.NOT_EQUAL)
+
     def test_invalid(self):
         with self.assertRaises(ValueError):
             self._call_fut("?")
diff --git a/tests/unit/v1/testdata/query-invalid-operator.json b/tests/unit/v1/testdata/query-invalid-operator.json
index 064164dc0..c53e5c2bd 100644
--- a/tests/unit/v1/testdata/query-invalid-operator.json
+++ b/tests/unit/v1/testdata/query-invalid-operator.json
@@ -2,7 +2,7 @@
   "tests": [
     {
       "description": "query: invalid operator in Where clause",
-      "comment": "The !=  operator is not supported.",
+      "comment": "The |~|  operator is not supported.",
       "query": {
         "collPath": "projects/projectID/databases/(default)/documents/C",
         "clauses": [
@@ -13,7 +13,7 @@
                   "a"
                 ]
               },
-              "op": "!=",
+              "op": "|~|",
               "jsonValue": "4"
             }
           }