diff --git a/api_core/google/api_core/protobuf_helpers.py b/api_core/google/api_core/protobuf_helpers.py
index 6031ff0e476f..fbe1a82db4d6 100644
--- a/api_core/google/api_core/protobuf_helpers.py
+++ b/api_core/google/api_core/protobuf_helpers.py
@@ -19,6 +19,8 @@
 
 from google.protobuf.message import Message
 
+_SENTINEL = object()
+
 
 def from_any_pb(pb_type, any_pb):
     """Converts an ``Any`` protobuf to the specified message type.
@@ -44,11 +46,13 @@ def from_any_pb(pb_type, any_pb):
 
 
 def check_oneof(**kwargs):
-    """Raise ValueError if more than one keyword argument is not none.
+    """Raise ValueError if more than one keyword argument is not ``None``.
+
     Args:
         kwargs (dict): The keyword arguments sent to the function.
+
     Raises:
-        ValueError: If more than one entry in kwargs is not none.
+        ValueError: If more than one entry in ``kwargs`` is not ``None``.
     """
     # Sanity check: If no keyword arguments were sent, this is fine.
     if not kwargs:
@@ -62,10 +66,12 @@ def check_oneof(**kwargs):
 
 
 def get_messages(module):
-    """Return a dictionary of message names and objects.
+    """Discovers all protobuf Message classes in a given import module.
+
     Args:
-        module (module): A Python module; dir() will be run against this
+        module (module): A Python module; :func:`dir` will be run against this
             module to find Message subclasses.
+
     Returns:
         dict[str, Message]: A dictionary with the Message class names as
             keys, and the Message subclasses themselves as values.
@@ -76,3 +82,168 @@ def get_messages(module):
         if inspect.isclass(candidate) and issubclass(candidate, Message):
             answer[name] = candidate
     return answer
+
+
+def _resolve_subkeys(key, separator='.'):
+    """Resolve a potentially nested key.
+
+    If the key contains the ``separator`` (e.g. ``.``) then the key will be
+    split on the first instance of the subkey::
+
+       >>> _resolve_subkeys('a.b.c')
+       ('a', 'b.c')
+       >>> _resolve_subkeys('d|e|f', separator='|')
+       ('d', 'e|f')
+
+    If not, the subkey will be :data:`None`::
+
+        >>> _resolve_subkeys('foo')
+        ('foo', None)
+
+    Args:
+        key (str): A string that may or may not contain the separator.
+        separator (str): The namespace separator. Defaults to `.`.
+
+    Returns:
+        Tuple[str, str]: The key and subkey(s).
+    """
+    parts = key.split(separator, 1)
+
+    if len(parts) > 1:
+        return parts
+    else:
+        return parts[0], None
+
+
+def get(msg_or_dict, key, default=_SENTINEL):
+    """Retrieve a key's value from a protobuf Message or dictionary.
+
+    Args:
+        mdg_or_dict (Union[~google.protobuf.message.Message, Mapping]): the
+            object.
+        key (str): The key to retrieve from the object.
+        default (Any): If the key is not present on the object, and a default
+            is set, returns that default instead. A type-appropriate falsy
+            default is generally recommended, as protobuf messages almost
+            always have default values for unset values and it is not always
+            possible to tell the difference between a falsy value and an
+            unset one. If no default is set then :class:`KeyError` will be
+            raised if the key is not present in the object.
+
+    Returns:
+        Any: The return value from the underlying Message or dict.
+
+    Raises:
+        KeyError: If the key is not found. Note that, for unset values,
+            messages and dictionaries may not have consistent behavior.
+        TypeError: If ``msg_or_dict`` is not a Message or Mapping.
+    """
+    # We may need to get a nested key. Resolve this.
+    key, subkey = _resolve_subkeys(key)
+
+    # Attempt to get the value from the two types of objects we know about.
+    # If we get something else, complain.
+    if isinstance(msg_or_dict, Message):
+        answer = getattr(msg_or_dict, key, default)
+    elif isinstance(msg_or_dict, collections.Mapping):
+        answer = msg_or_dict.get(key, default)
+    else:
+        raise TypeError(
+            'get() expected a dict or protobuf message, got {!r}.'.format(
+                type(msg_or_dict)))
+
+    # If the object we got back is our sentinel, raise KeyError; this is
+    # a "not found" case.
+    if answer is _SENTINEL:
+        raise KeyError(key)
+
+    # If a subkey exists, call this method recursively against the answer.
+    if subkey is not None and answer is not default:
+        return get(answer, subkey, default=default)
+
+    return answer
+
+
+def _set_field_on_message(msg, key, value):
+    """Set helper for protobuf Messages."""
+    # Attempt to set the value on the types of objects we know how to deal
+    # with.
+    if isinstance(value, (collections.MutableSequence, tuple)):
+        # Clear the existing repeated protobuf message of any elements
+        # currently inside it.
+        while getattr(msg, key):
+            getattr(msg, key).pop()
+
+        # Write our new elements to the repeated field.
+        for item in value:
+            if isinstance(item, collections.Mapping):
+                getattr(msg, key).add(**item)
+            else:
+                # protobuf's RepeatedCompositeContainer doesn't support
+                # append.
+                getattr(msg, key).extend([item])
+    elif isinstance(value, collections.Mapping):
+        # Assign the dictionary values to the protobuf message.
+        for item_key, item_value in value.items():
+            set(getattr(msg, key), item_key, item_value)
+    elif isinstance(value, Message):
+        getattr(msg, key).CopyFrom(value)
+    else:
+        setattr(msg, key, value)
+
+
+def set(msg_or_dict, key, value):
+    """Set a key's value on a protobuf Message or dictionary.
+
+    Args:
+        msg_or_dict (Union[~google.protobuf.message.Message, Mapping]): the
+            object.
+        key (str): The key to set.
+        value (Any): The value to set.
+
+    Raises:
+        TypeError: If ``msg_or_dict`` is not a Message or dictionary.
+    """
+    # Sanity check: Is our target object valid?
+    if not isinstance(msg_or_dict, (collections.MutableMapping, Message)):
+        raise TypeError(
+            'set() expected a dict or protobuf message, got {!r}.'.format(
+                type(msg_or_dict)))
+
+    # We may be setting a nested key. Resolve this.
+    basekey, subkey = _resolve_subkeys(key)
+
+    # If a subkey exists, then get that object and call this method
+    # recursively against it using the subkey.
+    if subkey is not None:
+        if isinstance(msg_or_dict, collections.MutableMapping):
+            msg_or_dict.setdefault(basekey, {})
+        set(get(msg_or_dict, basekey), subkey, value)
+        return
+
+    if isinstance(msg_or_dict, collections.MutableMapping):
+        msg_or_dict[key] = value
+    else:
+        _set_field_on_message(msg_or_dict, key, value)
+
+
+def setdefault(msg_or_dict, key, value):
+    """Set the key on a protobuf Message or dictionary to a given value if the
+    current value is falsy.
+
+    Because protobuf Messages do not distinguish between unset values and
+    falsy ones particularly well (by design), this method treats any falsy
+    value (e.g. 0, empty list) as a target to be overwritten, on both Messages
+    and dictionaries.
+
+    Args:
+        msg_or_dict (Union[~google.protobuf.message.Message, Mapping]): the
+            object.
+        key (str): The key on the object in question.
+        value (Any): The value to set.
+
+    Raises:
+        TypeError: If ``msg_or_dict`` is not a Message or dictionary.
+    """
+    if not get(msg_or_dict, key, default=None):
+        set(msg_or_dict, key, value)
diff --git a/api_core/tests/unit/test_protobuf_helpers.py b/api_core/tests/unit/test_protobuf_helpers.py
index b9aca76a9bcd..8f86aa4401d5 100644
--- a/api_core/tests/unit/test_protobuf_helpers.py
+++ b/api_core/tests/unit/test_protobuf_helpers.py
@@ -14,8 +14,11 @@
 
 import pytest
 
+from google.api import http_pb2
 from google.api_core import protobuf_helpers
+from google.longrunning import operations_pb2
 from google.protobuf import any_pb2
+from google.protobuf import timestamp_pb2
 from google.protobuf.message import Message
 from google.type import date_pb2
 from google.type import timeofday_pb2
@@ -65,3 +68,165 @@ def test_get_messages():
     # Ensure that no non-Message objects were exported.
     for value in answer.values():
         assert issubclass(value, Message)
+
+
+def test_get_dict_absent():
+    with pytest.raises(KeyError):
+        assert protobuf_helpers.get({}, 'foo')
+
+
+def test_get_dict_present():
+    assert protobuf_helpers.get({'foo': 'bar'}, 'foo') == 'bar'
+
+
+def test_get_dict_default():
+    assert protobuf_helpers.get({}, 'foo', default='bar') == 'bar'
+
+
+def test_get_dict_nested():
+    assert protobuf_helpers.get({'foo': {'bar': 'baz'}}, 'foo.bar') == 'baz'
+
+
+def test_get_dict_nested_default():
+    assert protobuf_helpers.get({}, 'foo.baz', default='bacon') == 'bacon'
+    assert (
+        protobuf_helpers.get({'foo': {}}, 'foo.baz', default='bacon') ==
+        'bacon')
+
+
+def test_get_msg_sentinel():
+    msg = timestamp_pb2.Timestamp()
+    with pytest.raises(KeyError):
+        assert protobuf_helpers.get(msg, 'foo')
+
+
+def test_get_msg_present():
+    msg = timestamp_pb2.Timestamp(seconds=42)
+    assert protobuf_helpers.get(msg, 'seconds') == 42
+
+
+def test_get_msg_default():
+    msg = timestamp_pb2.Timestamp()
+    assert protobuf_helpers.get(msg, 'foo', default='bar') == 'bar'
+
+
+def test_invalid_object():
+    with pytest.raises(TypeError):
+        protobuf_helpers.get(object(), 'foo', 'bar')
+
+
+def test_set_dict():
+    mapping = {}
+    protobuf_helpers.set(mapping, 'foo', 'bar')
+    assert mapping == {'foo': 'bar'}
+
+
+def test_set_msg():
+    msg = timestamp_pb2.Timestamp()
+    protobuf_helpers.set(msg, 'seconds', 42)
+    assert msg.seconds == 42
+
+
+def test_set_dict_nested():
+    mapping = {}
+    protobuf_helpers.set(mapping, 'foo.bar', 'baz')
+    assert mapping == {'foo': {'bar': 'baz'}}
+
+
+def test_set_invalid_object():
+    with pytest.raises(TypeError):
+        protobuf_helpers.set(object(), 'foo', 'bar')
+
+
+def test_set_list():
+    list_ops_response = operations_pb2.ListOperationsResponse()
+
+    protobuf_helpers.set(list_ops_response, 'operations', [
+        {'name': 'foo'},
+        operations_pb2.Operation(name='bar'),
+    ])
+
+    assert len(list_ops_response.operations) == 2
+
+    for operation in list_ops_response.operations:
+        assert isinstance(operation, operations_pb2.Operation)
+
+    assert list_ops_response.operations[0].name == 'foo'
+    assert list_ops_response.operations[1].name == 'bar'
+
+
+def test_set_list_clear_existing():
+    list_ops_response = operations_pb2.ListOperationsResponse(
+        operations=[{'name': 'baz'}],
+    )
+
+    protobuf_helpers.set(list_ops_response, 'operations', [
+        {'name': 'foo'},
+        operations_pb2.Operation(name='bar'),
+    ])
+
+    assert len(list_ops_response.operations) == 2
+    for operation in list_ops_response.operations:
+        assert isinstance(operation, operations_pb2.Operation)
+    assert list_ops_response.operations[0].name == 'foo'
+    assert list_ops_response.operations[1].name == 'bar'
+
+
+def test_set_msg_with_msg_field():
+    rule = http_pb2.HttpRule()
+    pattern = http_pb2.CustomHttpPattern(kind='foo', path='bar')
+
+    protobuf_helpers.set(rule, 'custom', pattern)
+
+    assert rule.custom.kind == 'foo'
+    assert rule.custom.path == 'bar'
+
+
+def test_set_msg_with_dict_field():
+    rule = http_pb2.HttpRule()
+    pattern = {'kind': 'foo', 'path': 'bar'}
+
+    protobuf_helpers.set(rule, 'custom', pattern)
+
+    assert rule.custom.kind == 'foo'
+    assert rule.custom.path == 'bar'
+
+
+def test_set_msg_nested_key():
+    rule = http_pb2.HttpRule(
+        custom=http_pb2.CustomHttpPattern(kind='foo', path='bar'))
+
+    protobuf_helpers.set(rule, 'custom.kind', 'baz')
+
+    assert rule.custom.kind == 'baz'
+    assert rule.custom.path == 'bar'
+
+
+def test_setdefault_dict_unset():
+    mapping = {}
+    protobuf_helpers.setdefault(mapping, 'foo', 'bar')
+    assert mapping == {'foo': 'bar'}
+
+
+def test_setdefault_dict_falsy():
+    mapping = {'foo': None}
+    protobuf_helpers.setdefault(mapping, 'foo', 'bar')
+    assert mapping == {'foo': 'bar'}
+
+
+def test_setdefault_dict_truthy():
+    mapping = {'foo': 'bar'}
+    protobuf_helpers.setdefault(mapping, 'foo', 'baz')
+    assert mapping == {'foo': 'bar'}
+
+
+def test_setdefault_pb2_falsy():
+    operation = operations_pb2.Operation()
+    protobuf_helpers.setdefault(operation, 'name', 'foo')
+    assert operation.name == 'foo'
+
+
+def test_setdefault_pb2_truthy():
+    operation = operations_pb2.Operation(name='bar')
+    protobuf_helpers.setdefault(operation, 'name', 'foo')
+    assert operation.name == 'bar'