diff --git a/gapic/ads-templates/%namespace/%name/%version/%sub/types/_message.py.j2 b/gapic/ads-templates/%namespace/%name/%version/%sub/types/_message.py.j2
index a8119827b8..15bf3ea4ab 100644
--- a/gapic/ads-templates/%namespace/%name/%version/%sub/types/_message.py.j2
+++ b/gapic/ads-templates/%namespace/%name/%version/%sub/types/_message.py.j2
@@ -43,6 +43,7 @@ class {{ message.name }}({{ p }}.Message):
     {% else -%}
     {{ field.name }} = {{ p }}.{% if field.repeated %}Repeated{% endif %}Field(
         {{- p }}.{{ field.proto_type }}, number={{ field.number }}
+    {% if field.oneof %}, oneof='{{ field.oneof }}'{% endif %}
     {%- if field.enum or field.message %},
         {{ field.proto_type.lower() }}={{ field.type.ident.rel(message.ident) }},
     {% endif %})
diff --git a/gapic/schema/api.py b/gapic/schema/api.py
index cc9b9cf1f0..df3e1daa8e 100644
--- a/gapic/schema/api.py
+++ b/gapic/schema/api.py
@@ -34,6 +34,7 @@
 from gapic.schema import wrappers
 from gapic.schema import naming as api_naming
 from gapic.utils import cached_property
+from gapic.utils import nth
 from gapic.utils import to_snake_case
 from gapic.utils import RESERVED_NAMES
 
@@ -556,14 +557,42 @@ def _load_children(self,
             answer[wrapped.name] = wrapped
         return answer
 
+    def _get_oneofs(self,
+                    oneof_pbs: Sequence[descriptor_pb2.OneofDescriptorProto],
+                    address: metadata.Address, path: Tuple[int, ...],
+                    ) -> Dict[str, wrappers.Oneof]:
+        """Return a dictionary of wrapped oneofs for the given message.
+
+        Args:
+            oneof_fields (Sequence[~.descriptor_pb2.OneofDescriptorProto]): A
+                sequence of protobuf field objects.
+            address (~.metadata.Address): An address object denoting the
+                location of these oneofs.
+            path (Tuple[int]): The source location path thus far, as
+                understood by ``SourceCodeInfo.Location``.
+
+        Returns:
+            Mapping[str, ~.wrappers.Oneof]: A ordered mapping of
+                :class:`~.wrappers.Oneof` objects.
+        """
+        # Iterate over the oneofs and collect them into a dictionary.
+        answer = collections.OrderedDict(
+            (oneof_pb.name, wrappers.Oneof(oneof_pb=oneof_pb))
+            for i, oneof_pb in enumerate(oneof_pbs)
+        )
+
+        # Done; return the answer.
+        return answer
+
     def _get_fields(self,
                     field_pbs: Sequence[descriptor_pb2.FieldDescriptorProto],
                     address: metadata.Address, path: Tuple[int, ...],
+                    oneofs: Optional[Dict[str, wrappers.Oneof]] = None
                     ) -> Dict[str, wrappers.Field]:
         """Return a dictionary of wrapped fields for the given message.
 
         Args:
-            fields (Sequence[~.descriptor_pb2.FieldDescriptorProto]): A
+            field_pbs (Sequence[~.descriptor_pb2.FieldDescriptorProto]): A
                 sequence of protobuf field objects.
             address (~.metadata.Address): An address object denoting the
                 location of these fields.
@@ -585,7 +614,13 @@ def _get_fields(self,
         # first) and this will be None. This case is addressed in the
         # `_load_message` method.
         answer: Dict[str, wrappers.Field] = collections.OrderedDict()
-        for field_pb, i in zip(field_pbs, range(0, sys.maxsize)):
+        for i, field_pb in enumerate(field_pbs):
+            is_oneof = oneofs and field_pb.oneof_index > 0
+            oneof_name = nth(
+                (oneofs or {}).keys(),
+                field_pb.oneof_index
+            ) if is_oneof else None
+
             answer[field_pb.name] = wrappers.Field(
                 field_pb=field_pb,
                 enum=self.api_enums.get(field_pb.type_name.lstrip('.')),
@@ -594,6 +629,7 @@ def _get_fields(self,
                     address=address.child(field_pb.name, path + (i,)),
                     documentation=self.docs.get(path + (i,), self.EMPTY),
                 ),
+                oneof=oneof_name,
             )
 
         # Done; return the answer.
@@ -779,19 +815,25 @@ def _load_message(self,
             loader=self._load_message,
             path=path + (3,),
         )
-        # self._load_children(message.oneof_decl, loader=self._load_field,
-        #                     address=nested_addr, info=info.get(8, {}))
+
+        oneofs = self._get_oneofs(
+            message_pb.oneof_decl,
+            address=address,
+            path=path + (7,),
+        )
 
         # Create a dictionary of all the fields for this message.
         fields = self._get_fields(
             message_pb.field,
             address=address,
             path=path + (2,),
+            oneofs=oneofs,
         )
         fields.update(self._get_fields(
             message_pb.extension,
             address=address,
             path=path + (6,),
+            oneofs=oneofs,
         ))
 
         # Create a message correspoding to this descriptor.
@@ -804,6 +846,7 @@ def _load_message(self,
                 address=address,
                 documentation=self.docs.get(path, self.EMPTY),
             ),
+            oneofs=oneofs,
         )
         return self.proto_messages[address.proto]
 
diff --git a/gapic/schema/wrappers.py b/gapic/schema/wrappers.py
index 6f7e041f16..1061620378 100644
--- a/gapic/schema/wrappers.py
+++ b/gapic/schema/wrappers.py
@@ -54,6 +54,7 @@ class Field:
     meta: metadata.Metadata = dataclasses.field(
         default_factory=metadata.Metadata,
     )
+    oneof: Optional[str] = None
 
     def __getattr__(self, name):
         return getattr(self.field_pb, name)
@@ -206,6 +207,15 @@ def with_context(self, *, collisions: FrozenSet[str]) -> 'Field':
         )
 
 
+@dataclasses.dataclass(frozen=True)
+class Oneof:
+    """Description of a field."""
+    oneof_pb: descriptor_pb2.OneofDescriptorProto
+
+    def __getattr__(self, name):
+        return getattr(self.oneof_pb, name)
+
+
 @dataclasses.dataclass(frozen=True)
 class MessageType:
     """Description of a message (defined with the ``message`` keyword)."""
@@ -220,6 +230,7 @@ class MessageType:
     meta: metadata.Metadata = dataclasses.field(
         default_factory=metadata.Metadata,
     )
+    oneofs: Optional[Mapping[str, 'Oneof']] = None
 
     def __getattr__(self, name):
         return getattr(self.message_pb, name)
diff --git a/gapic/templates/%namespace/%name_%version/%sub/types/_message.py.j2 b/gapic/templates/%namespace/%name_%version/%sub/types/_message.py.j2
index e9586108c0..5a1eb5fcc6 100644
--- a/gapic/templates/%namespace/%name_%version/%sub/types/_message.py.j2
+++ b/gapic/templates/%namespace/%name_%version/%sub/types/_message.py.j2
@@ -38,14 +38,15 @@ class {{ message.name }}({{ p }}.Message):
         {{- p }}.{{ key_field.proto_type }}, {{ p }}.{{ value_field.proto_type }}, number={{ field.number }}
     {%- if value_field.enum or value_field.message %},
         {{ value_field.proto_type.lower() }}={{ value_field.type.ident.rel(message.ident) }},
-    {% endif %})
+    {% endif %})                {# enum or message#}
     {% endwith -%}
-    {% else -%}
+    {% else -%}                 {# field.map #}
     {{ field.name }} = {{ p }}.{% if field.repeated %}Repeated{% endif %}Field(
         {{- p }}.{{ field.proto_type }}, number={{ field.number }}
+    {% if field.oneof %}, oneof='{{ field.oneof }}'{% endif %}
     {%- if field.enum or field.message %},
         {{ field.proto_type.lower() }}={{ field.type.ident.rel(message.ident) }},
-    {% endif %})
-    {% endif -%}
-    {% endfor -%}
+    {% endif %})                {# enum or message #}
+    {% endif -%}                {# field.map #}
+    {% endfor -%} {# for field in message.fields.values#}
 {{ '\n\n' }}
diff --git a/gapic/templates/noxfile.py.j2 b/gapic/templates/noxfile.py.j2
index d31a325e2f..5fde488f00 100644
--- a/gapic/templates/noxfile.py.j2
+++ b/gapic/templates/noxfile.py.j2
@@ -20,7 +20,7 @@ def unit(session):
         '--cov-config=.coveragerc',
         '--cov-report=term',
         '--cov-report=html',
-        os.path.join('tests', 'unit', '{{ api.naming.versioned_module_name }}'),
+        os.path.join('tests', 'unit',)
     )
 
 
diff --git a/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2 b/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2
index c21846a4ac..f561d927e1 100644
--- a/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2
+++ b/gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2
@@ -288,9 +288,9 @@ def test_{{ method.name|snake_case }}(transport: str = 'grpc'):
         call.return_value = iter([{{ method.output.ident }}()])
         {% else -%}
         call.return_value = {{ method.output.ident }}(
-            {%- for field in method.output.fields.values() | rejectattr('message') %}
+            {%- for field in method.output.fields.values() | rejectattr('message')%}{% if not (field.oneof and not field.proto3_optional) %}
             {{ field.name }}={{ field.mock_value }},
-            {%- endfor %}
+            {% endif %}{%- endfor %}
         )
         {% endif -%}
         {% if method.client_streaming %}
@@ -318,7 +318,7 @@ def test_{{ method.name|snake_case }}(transport: str = 'grpc'):
         assert isinstance(message, {{ method.output.ident }})
     {% else -%}
     assert isinstance(response, {{ method.client_output.ident }})
-    {% for field in method.output.fields.values() | rejectattr('message') -%}
+    {% for field in method.output.fields.values() | rejectattr('message') -%}{% if not (field.oneof and not field.proto3_optional) %}
     {% if field.field_pb.type in [1, 2] -%} {# Use approx eq for floats -#}
     assert math.isclose(response.{{ field.name }}, {{ field.mock_value }}, rel_tol=1e-6)
     {% elif field.field_pb.type == 8 -%} {# Use 'is' for bools #}
@@ -326,6 +326,7 @@ def test_{{ method.name|snake_case }}(transport: str = 'grpc'):
     {% else -%}
     assert response.{{ field.name }} == {{ field.mock_value }}
     {% endif -%}
+    {% endif -%} {# end oneof/optional #}
     {% endfor %}
     {% endif %}
 
@@ -368,8 +369,9 @@ async def test_{{ method.name|snake_case }}_async(transport: str = 'grpc_asyncio
             {%- else -%}
                 grpc_helpers_async.FakeStreamUnaryCall
             {%- endif -%}({{ method.output.ident }}(
-            {%- for field in method.output.fields.values() | rejectattr('message') %}
+            {%- for field in method.output.fields.values() | rejectattr('message') %}{% if not (field.oneof and not field.proto3_optional) %}
             {{ field.name }}={{ field.mock_value }},
+            {%- endif %}
             {%- endfor %}
         ))
         {% endif -%}
@@ -400,7 +402,7 @@ async def test_{{ method.name|snake_case }}_async(transport: str = 'grpc_asyncio
     assert isinstance(message, {{ method.output.ident }})
     {% else -%}
     assert isinstance(response, {{ method.client_output_async.ident }})
-    {% for field in method.output.fields.values() | rejectattr('message') -%}
+    {% for field in method.output.fields.values() | rejectattr('message') -%}{% if not (field.oneof and not field.proto3_optional) %}
     {% if field.field_pb.type in [1, 2] -%} {# Use approx eq for floats -#}
     assert math.isclose(response.{{ field.name }}, {{ field.mock_value }}, rel_tol=1e-6)
     {% elif field.field_pb.type == 8 -%} {# Use 'is' for bools #}
@@ -408,6 +410,7 @@ async def test_{{ method.name|snake_case }}_async(transport: str = 'grpc_asyncio
     {% else -%}
     assert response.{{ field.name }} == {{ field.mock_value }}
     {% endif -%}
+    {% endif -%} {# oneof/optional #}
     {% endfor %}
     {% endif %}
 
diff --git a/gapic/utils/__init__.py b/gapic/utils/__init__.py
index 315c575e2b..905fcbdec2 100644
--- a/gapic/utils/__init__.py
+++ b/gapic/utils/__init__.py
@@ -15,6 +15,7 @@
 from gapic.utils.cache import cached_property
 from gapic.utils.case import to_snake_case
 from gapic.utils.code import empty
+from gapic.utils.code import nth
 from gapic.utils.code import partition
 from gapic.utils.doc import doc
 from gapic.utils.filename import to_valid_filename
@@ -29,6 +30,7 @@
     'cached_property',
     'doc',
     'empty',
+    'nth',
     'partition',
     'RESERVED_NAMES',
     'rst',
diff --git a/gapic/utils/code.py b/gapic/utils/code.py
index 27458a999c..15f327983c 100644
--- a/gapic/utils/code.py
+++ b/gapic/utils/code.py
@@ -12,7 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import (Callable, Iterable, List, Tuple, TypeVar)
+from typing import (Callable, Iterable, List, Optional, Tuple, TypeVar)
+import itertools
 
 
 def empty(content: str) -> bool:
@@ -50,3 +51,15 @@ def partition(predicate: Callable[[T], bool],
 
     # Returns trueList, falseList
     return results[1], results[0]
+
+
+def nth(iterable: Iterable[T], n: int, default: Optional[T] = None) -> Optional[T]:
+    """Return the nth element of an iterable or a default value.
+
+    Args
+        iterable (Iterable(T)): An iterable on any type.
+        n (int):                The 'index' of the lement to retrieve.
+        default (Optional(T)):  An optional default elemnt if the iterable has
+                                 fewer than n elements.
+    """
+    return next(itertools.islice(iterable, n, None), default)
diff --git a/test_utils/test_utils.py b/test_utils/test_utils.py
index 697d08e8df..89fd735142 100644
--- a/test_utils/test_utils.py
+++ b/test_utils/test_utils.py
@@ -200,6 +200,7 @@ def make_field(
     message: wrappers.MessageType = None,
     enum: wrappers.EnumType = None,
     meta: metadata.Metadata = None,
+    oneof: str = None,
     **kwargs
 ) -> wrappers.Field:
     T = desc.FieldDescriptorProto.Type
@@ -223,11 +224,13 @@ def make_field(
         number=number,
         **kwargs
     )
+
     return wrappers.Field(
         field_pb=field_pb,
         enum=enum,
         message=message,
         meta=meta or metadata.Metadata(),
+        oneof=oneof,
     )
 
 
@@ -322,20 +325,28 @@ def make_enum_pb2(
 def make_message_pb2(
         name: str,
         fields: tuple = (),
+        oneof_decl: tuple = (),
         **kwargs
 ) -> desc.DescriptorProto:
-    return desc.DescriptorProto(name=name, field=fields, **kwargs)
+    return desc.DescriptorProto(name=name, field=fields, oneof_decl=oneof_decl, **kwargs)
 
 
 def make_field_pb2(name: str, number: int,
                    type: int = 11,  # 11 == message
                    type_name: str = None,
+                   oneof_index: int = None
                    ) -> desc.FieldDescriptorProto:
     return desc.FieldDescriptorProto(
         name=name,
         number=number,
         type=type,
         type_name=type_name,
+        oneof_index=oneof_index,
+    )
+
+def make_oneof_pb2(name: str) -> desc.OneofDescriptorProto:
+    return desc.OneofDescriptorProto(
+        name=name,
     )
 
 
diff --git a/tests/unit/schema/test_api.py b/tests/unit/schema/test_api.py
index 8dc1760cd8..b3f023054c 100644
--- a/tests/unit/schema/test_api.py
+++ b/tests/unit/schema/test_api.py
@@ -34,6 +34,7 @@
     make_file_pb2,
     make_message_pb2,
     make_naming,
+    make_oneof_pb2,
 )
 
 
@@ -239,6 +240,45 @@ def test_proto_keyword_fname():
     }
 
 
+def test_proto_oneof():
+    # Put together a couple of minimal protos.
+    fd = (
+        make_file_pb2(
+            name='dep.proto',
+            package='google.dep',
+            messages=(make_message_pb2(name='ImportedMessage', fields=()),),
+        ),
+        make_file_pb2(
+            name='foo.proto',
+            package='google.example.v1',
+            messages=(
+                make_message_pb2(name='Foo', fields=()),
+                make_message_pb2(
+                    name='Bar',
+                    fields=(
+                        make_field_pb2(name='imported_message', number=1,
+                                   type_name='.google.dep.ImportedMessage',
+                                   oneof_index=0),
+                        make_field_pb2(
+                            name='primitive', number=2, type=1, oneof_index=0),
+                    ),
+                    oneof_decl=(
+                        make_oneof_pb2(name="value_type"),
+                    )
+                )
+            )
+        )
+    )
+
+    # Create an API with those protos.
+    api_schema = api.API.build(fd, package='google.example.v1')
+    proto = api_schema.protos['foo.proto']
+    assert proto.names == {'imported_message', 'Bar', 'primitive', 'Foo'}
+    oneofs = proto.messages["google.example.v1.Bar"].oneofs
+    assert len(oneofs) == 1
+    assert "value_type" in oneofs.keys()
+
+
 def test_proto_names_import_collision():
     # Put together a couple of minimal protos.
     fd = (
diff --git a/tests/unit/schema/wrappers/test_field.py b/tests/unit/schema/wrappers/test_field.py
index 7104c735be..3cdcaf9bcf 100644
--- a/tests/unit/schema/wrappers/test_field.py
+++ b/tests/unit/schema/wrappers/test_field.py
@@ -153,6 +153,13 @@ def test_mock_value_int():
     assert field.mock_value == '728'
 
 
+def test_oneof():
+    REP = descriptor_pb2.FieldDescriptorProto.Label.Value('LABEL_REPEATED')
+
+    field = make_field(oneof="oneof_name")
+    assert field.oneof == "oneof_name"
+
+
 def test_mock_value_float():
     field = make_field(name='foo_bar', type='TYPE_DOUBLE')
     assert field.mock_value == '0.728'
diff --git a/tests/unit/schema/wrappers/test_oneof.py b/tests/unit/schema/wrappers/test_oneof.py
new file mode 100644
index 0000000000..90fe2546ce
--- /dev/null
+++ b/tests/unit/schema/wrappers/test_oneof.py
@@ -0,0 +1,35 @@
+# Copyright 2018 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import collections
+
+import pytest
+
+from google.api import field_behavior_pb2
+from google.protobuf import descriptor_pb2
+
+from gapic.schema import metadata
+from gapic.schema import wrappers
+
+from test_utils.test_utils import (
+    make_oneof_pb2,
+)
+
+
+def test_wrapped_oneof():
+    oneof_pb = make_oneof_pb2("oneof_name")
+    wrapped = wrappers.Oneof(oneof_pb=oneof_pb)
+
+    assert wrapped.oneof_pb == oneof_pb
+    assert wrapped.name == oneof_pb.name
diff --git a/tests/unit/utils/test_code.py b/tests/unit/utils/test_code.py
index 1069443f7b..5f18679d6f 100644
--- a/tests/unit/utils/test_code.py
+++ b/tests/unit/utils/test_code.py
@@ -34,3 +34,12 @@ def test_empty_whitespace_comments():
 
 def test_empty_code():
     assert not code.empty('import this')
+
+
+def test_nth():
+    # list
+    assert code.nth([i * i for i in range(20)], 4) == 16
+    # generator
+    assert code.nth((i * i for i in range(20)), 4) == 16
+    # default
+    assert code.nth((i * i for i in range(20)), 30, 2112) == 2112