diff --git a/bumble/device.py b/bumble/device.py
index 72fd755..258a43d 100644
--- a/bumble/device.py
+++ b/bumble/device.py
@@ -889,7 +889,7 @@ def host_event_handler(function):
 # List of host event handlers for the Device class.
 # (we define this list outside the class, because referencing a class in method
 #  decorators is not straightforward)
-device_host_event_handlers: list[str] = []
+device_host_event_handlers: List[str] = []
 
 
 # -----------------------------------------------------------------------------
diff --git a/bumble/gatt.py b/bumble/gatt.py
index e57f0a6..d99df81 100644
--- a/bumble/gatt.py
+++ b/bumble/gatt.py
@@ -205,8 +205,16 @@ class Service(Attribute):
     '''
 
     uuid: UUID
+    characteristics: List[Characteristic]
+    included_services: List[Service]
 
-    def __init__(self, uuid, characteristics: list[Characteristic], primary=True):
+    def __init__(
+        self,
+        uuid,
+        characteristics: List[Characteristic],
+        included_services: List[Service] = [],
+        primary=True,
+    ):
         # Convert the uuid to a UUID object if it isn't already
         if isinstance(uuid, str):
             uuid = UUID(uuid)
@@ -219,7 +227,7 @@ class Service(Attribute):
             uuid.to_pdu_bytes(),
         )
         self.uuid = uuid
-        # self.included_services = []
+        self.included_services = included_services[:]
         self.characteristics = characteristics[:]
         self.primary = primary
 
@@ -253,6 +261,33 @@ class TemplateService(Service):
         super().__init__(self.UUID, characteristics, primary)
 
 
+# -----------------------------------------------------------------------------
+class IncludedServiceDeclaration(Attribute):
+    '''
+    See Vol 3, Part G - 3.2 INCLUDE DEFINITION
+    '''
+
+    service: Service
+
+    def __init__(self, service):
+        declaration_bytes = struct.pack(
+            '<HH2s', service.handle, service.end_group_handle, service.uuid.to_bytes()
+        )
+        super().__init__(
+            GATT_INCLUDE_ATTRIBUTE_TYPE, Attribute.READABLE, declaration_bytes
+        )
+        self.service = service
+
+    def __str__(self):
+        return (
+            f'IncludedServiceDefinition(handle=0x{self.handle:04X}, '
+            f'group_starting_handle=0x{self.service.handle:04X}, '
+            f'group_ending_handle=0x{self.service.end_group_handle:04X}, '
+            f'uuid={self.service.uuid}, '
+            f'{self.service.properties!s})'
+        )
+
+
 # -----------------------------------------------------------------------------
 class Characteristic(Attribute):
     '''
diff --git a/bumble/gatt_client.py b/bumble/gatt_client.py
index 35d8eb7..a33039e 100644
--- a/bumble/gatt_client.py
+++ b/bumble/gatt_client.py
@@ -63,6 +63,7 @@ from .gatt import (
     GATT_PRIMARY_SERVICE_ATTRIBUTE_TYPE,
     GATT_REQUEST_TIMEOUT,
     GATT_SECONDARY_SERVICE_ATTRIBUTE_TYPE,
+    GATT_INCLUDE_ATTRIBUTE_TYPE,
     Characteristic,
     ClientCharacteristicConfigurationBits,
 )
@@ -109,6 +110,7 @@ class AttributeProxy(EventEmitter):
 class ServiceProxy(AttributeProxy):
     uuid: UUID
     characteristics: List[CharacteristicProxy]
+    included_services: List[ServiceProxy]
 
     @staticmethod
     def from_client(service_class, client, service_uuid):
@@ -502,12 +504,69 @@ class Client:
 
         return services
 
-    async def discover_included_services(self, _service):
+    async def discover_included_services(
+        self, service: ServiceProxy
+    ) -> List[ServiceProxy]:
         '''
         See Vol 3, Part G - 4.5.1 Find Included Services
         '''
-        # TODO
-        return []
+
+        starting_handle = service.handle
+        ending_handle = service.end_group_handle
+
+        included_services: List[ServiceProxy] = []
+        while starting_handle <= ending_handle:
+            response = await self.send_request(
+                ATT_Read_By_Type_Request(
+                    starting_handle=starting_handle,
+                    ending_handle=ending_handle,
+                    attribute_type=GATT_INCLUDE_ATTRIBUTE_TYPE,
+                )
+            )
+            if response is None:
+                # TODO raise appropriate exception
+                return []
+
+            # Check if we reached the end of the iteration
+            if response.op_code == ATT_ERROR_RESPONSE:
+                if response.error_code != ATT_ATTRIBUTE_NOT_FOUND_ERROR:
+                    # Unexpected end
+                    logger.warning(
+                        '!!! unexpected error while discovering included services: '
+                        f'{HCI_Constant.error_name(response.error_code)}'
+                    )
+                    raise ATT_Error(
+                        error_code=response.error_code,
+                        message='Unexpected error while discovering included services',
+                    )
+                break
+
+            # Stop if for some reason the list was empty
+            if not response.attributes:
+                break
+
+            # Process all included services returned in this iteration
+            for attribute_handle, attribute_value in response.attributes:
+                if attribute_handle < starting_handle:
+                    # Something's not right
+                    logger.warning(f'bogus handle value: {attribute_handle}')
+                    return []
+
+                group_starting_handle, group_ending_handle = struct.unpack_from(
+                    '<HH', attribute_value
+                )
+                service_uuid = UUID.from_bytes(attribute_value[4:])
+                included_service = ServiceProxy(
+                    self, group_starting_handle, group_ending_handle, service_uuid, True
+                )
+
+                included_services.append(included_service)
+
+            # Move on to the next included services
+            starting_handle = response.attributes[-1][0] + 1
+
+        service.included_services = included_services
+        return included_services
 
     async def discover_characteristics(
         self, uuids, service: Optional[ServiceProxy]
diff --git a/bumble/gatt_server.py b/bumble/gatt_server.py
index 51f3ec0..3624905 100644
--- a/bumble/gatt_server.py
+++ b/bumble/gatt_server.py
@@ -68,6 +68,7 @@ from .gatt import (
     Characteristic,
     CharacteristicDeclaration,
     CharacteristicValue,
+    IncludedServiceDeclaration,
     Descriptor,
     Service,
 )
@@ -94,6 +95,7 @@ class Server(EventEmitter):
     def __init__(self, device):
         super().__init__()
         self.device = device
+        self.services = []
         self.attributes = []  # Attributes, ordered by increasing handle values
         self.attributes_by_handle = {}  # Map for fast attribute access by handle
         self.max_mtu = (
@@ -222,7 +224,14 @@ class Server(EventEmitter):
         # Add the service attribute to the DB
         self.add_attribute(service)
 
-        # TODO: add included services
+        # Add all included service
+        for included_service in service.included_services:
+            # Not registered yet, register the included service first.
+            if included_service not in self.services:
+                self.add_service(included_service)
+                # TODO: Handle circular service reference
+            include_declaration = IncludedServiceDeclaration(included_service)
+            self.add_attribute(include_declaration)
 
         # Add all characteristics
         for characteristic in service.characteristics:
@@ -274,6 +283,7 @@ class Server(EventEmitter):
 
         # Update the service group end
         service.end_group_handle = self.attributes[-1].handle
+        self.services.append(service)
 
     def add_services(self, services):
         for service in services:
diff --git a/tests/self_test.py b/tests/self_test.py
index 9105d2b..1a1a474 100644
--- a/tests/self_test.py
+++ b/tests/self_test.py
@@ -190,7 +190,9 @@ async def test_self_gatt():
 
     s1 = Service('8140E247-04F0-42C1-BC34-534C344DAFCA', [c1, c2, c3])
     s2 = Service('97210A0F-1875-4D05-9E5D-326EB171257A', [c4])
-    two_devices.devices[1].add_services([s1, s2])
+    s3 = Service('1853', [])
+    s4 = Service('3A12C182-14E2-4FE0-8C5B-65D7C569F9DB', [], included_services=[s2, s3])
+    two_devices.devices[1].add_services([s1, s2, s4])
 
     # Start
     await two_devices.devices[0].power_on()
@@ -225,6 +227,13 @@ async def test_self_gatt():
     assert result is not None
     assert result == c1.value
 
+    result = await peer.discover_service(s4.uuid)
+    assert len(result) == 1
+    result = await peer.discover_included_services(result[0])
+    assert len(result) == 2
+    # Service UUID is only present when the UUID is 16-bit Bluetooth UUID
+    assert result[1].uuid.to_bytes() == s3.uuid.to_bytes()
+
 
 # -----------------------------------------------------------------------------
 @pytest.mark.asyncio