diff --git a/HISTORY.md b/HISTORY.md
index b46758a1..a033806a 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -8,6 +8,7 @@
 * Added new function for **Life list** endpoint: `get_observation_taxonomy()`
 
 ### Modified Endpoints
+* Added support for passing a `requests.Session` object to all API request functions
 * Added a `photos` parameter `create_observation()` and `update_observation()` to upload photos
 * Added a `sounds` parameter `create_observation()` and `update_observation()` to upload sounds
 * Renamed `add_photo_to_observation()` to `upload_photos()`
diff --git a/pyinaturalist/api_docs/forge_utils.py b/pyinaturalist/api_docs/forge_utils.py
index 02812f85..72827c91 100644
--- a/pyinaturalist/api_docs/forge_utils.py
+++ b/pyinaturalist/api_docs/forge_utils.py
@@ -7,6 +7,8 @@
 from logging import getLogger
 from typing import Callable, List
 
+from requests import Session
+
 from pyinaturalist.constants import TemplateFunction
 
 logger = getLogger(__name__)
@@ -49,7 +51,7 @@ def copy_doc_signature(template_functions: List[TemplateFunction]) -> Callable:
         template_functions: Template functions containing docstrings and params to apply to the
             wrapped function
     """
-    template_functions += [_user_agent]
+    template_functions += [_user_agent, _session]
 
     def wrapper(func):
         # Modify docstring
@@ -147,8 +149,14 @@ def _get_combined_revision(target_function: Callable, template_functions: List[T
     return forge.sign(*fparams.values())
 
 
-# Param template that's added to every function signature by default
+# Param templates that are added to every function signature by default
 def _user_agent(user_agent: str = None):
     """
     user_agent: A custom user-agent string to provide to the iNaturalist API
     """
+
+
+def _session(session: Session = None):
+    """
+    session: Allows managing your own `Session object <https://docs.python-requests.org/en/latest/user/advanced/>`_
+    """
diff --git a/pyinaturalist/api_requests.py b/pyinaturalist/api_requests.py
index ca651aba..9942fe3c 100644
--- a/pyinaturalist/api_requests.py
+++ b/pyinaturalist/api_requests.py
@@ -6,11 +6,9 @@
 from typing import Dict
 from unittest.mock import Mock
 
-import requests
+from requests import Response, Session
 
 import pyinaturalist
-
-# from pyinaturalist.exceptions import TooManyRequests
 from pyinaturalist.api_docs import copy_signature
 from pyinaturalist.constants import (
     MAX_DELAY,
@@ -24,7 +22,7 @@
 from pyinaturalist.request_params import prepare_request
 
 # Mock response content to return in dry-run mode
-MOCK_RESPONSE = Mock(spec=requests.Response)
+MOCK_RESPONSE = Mock(spec=Response)
 MOCK_RESPONSE.json.return_value = {'results': [], 'total_results': 0, 'access_token': ''}
 
 logger = getLogger(__name__)
@@ -37,14 +35,13 @@ def request(
     access_token: str = None,
     user_agent: str = None,
     ids: MultiInt = None,
-    params: RequestParams = None,
     headers: Dict = None,
     json: Dict = None,
-    session: requests.Session = None,
+    session: Session = None,
     raise_for_status: bool = True,
     timeout: float = 5,
-    **kwargs,
-) -> requests.Response:
+    **params: RequestParams,
+) -> Response:
     """Wrapper around :py:func:`requests.request` that supports dry-run mode and rate-limiting,
     and adds appropriate headers.
 
@@ -52,15 +49,14 @@ def request(
         method: HTTP method
         url: Request URL
         access_token: access_token: the access token, as returned by :func:`get_access_token()`
-        user_agent: a user-agent string that will be passed to iNaturalist
+        user_agent: A custom user-agent string to provide to the iNaturalist API
         ids: One or more integer IDs used as REST resource(s) to request
-        params: Requests parameters
         headers: Request headers
         json: JSON request body
         session: Existing Session object to use instead of creating a new one
         timeout: Time (in seconds) to wait for a response from the server; if exceeded, a
             :py:exc:`requests.exceptions.Timeout` will be raised.
-        kwargs: Additional keyword arguments for :py:meth:`requests.Session.request`
+        params: All other keyword arguments are interpreted as request parameters
 
     Returns:
         API response
@@ -79,12 +75,12 @@ def request(
     # Run either real request or mock request depending on settings
     if is_dry_run_enabled(method):
         logger.debug('Dry-run mode enabled; mocking request')
-        log_request(method, url, params=params, headers=headers, **kwargs)
+        log_request(method, url, params=params, headers=headers)
         return MOCK_RESPONSE
     else:
         with ratelimit():
             response = session.request(
-                method, url, params=params, headers=headers, json=json, timeout=timeout, **kwargs
+                method, url, params=params, headers=headers, json=json, timeout=timeout
             )
         if raise_for_status:
             response.raise_for_status()
@@ -92,25 +88,25 @@ def request(
 
 
 @copy_signature(request, exclude='method')
-def delete(url: str, **kwargs) -> requests.Response:
+def delete(url: str, **kwargs) -> Response:
     """Wrapper around :py:func:`requests.delete` that supports dry-run mode and rate-limiting"""
     return request('DELETE', url, **kwargs)
 
 
 @copy_signature(request, exclude='method')
-def get(url: str, **kwargs) -> requests.Response:
+def get(url: str, **kwargs) -> Response:
     """Wrapper around :py:func:`requests.get` that supports dry-run mode and rate-limiting"""
     return request('GET', url, **kwargs)
 
 
 @copy_signature(request, exclude='method')
-def post(url: str, **kwargs) -> requests.Response:
+def post(url: str, **kwargs) -> Response:
     """Wrapper around :py:func:`requests.post` that supports dry-run mode and rate-limiting"""
     return request('POST', url, **kwargs)
 
 
 @copy_signature(request, exclude='method')
-def put(url: str, **kwargs) -> requests.Response:
+def put(url: str, **kwargs) -> Response:
     """Wrapper around :py:func:`requests.put` that supports dry-run mode and rate-limiting"""
     return request('PUT', url, **kwargs)
 
@@ -143,14 +139,14 @@ def get_limiter():
         return None
 
 
-def get_session() -> requests.Session:
+def get_session() -> Session:
     """Get a Session object that will be reused across requests to take advantage of connection
     pooling. This is especially relevant for large paginated requests. If used in a multi-threaded
     context (for example, a :py:class:`~concurrent.futures.ThreadPoolExecutor`), a separate session
     is used for each thread.
     """
     if not hasattr(thread_local, "session"):
-        thread_local.session = requests.Session()
+        thread_local.session = Session()
     return thread_local.session
 
 
diff --git a/pyinaturalist/auth.py b/pyinaturalist/auth.py
index 3688a283..87ee2664 100644
--- a/pyinaturalist/auth.py
+++ b/pyinaturalist/auth.py
@@ -53,7 +53,7 @@ def get_access_token(
         password: iNaturalist password (same as the one you use to login on inaturalist.org)
         app_id: OAuth2 application ID
         app_secret: OAuth2 application secret
-        user_agent: a user-agent string that will be passed to iNaturalist.
+        user_agent: A custom user-agent string to provide to the iNaturalist API
 
     Raises:
         :py:exc:`requests.HTTPError` (401) if credentials are invalid
diff --git a/pyinaturalist/request_params.py b/pyinaturalist/request_params.py
index 360d551f..34f5117d 100644
--- a/pyinaturalist/request_params.py
+++ b/pyinaturalist/request_params.py
@@ -51,17 +51,13 @@ def prepare_request(
     # Prepare request params
     params = preprocess_request_params(params)
 
-    # Prepare user and authentication headers
+    # Prepare user-agent and authentication headers
     headers = headers or {}
+    headers['User-Agent'] = user_agent or pyinaturalist.user_agent
     headers['Accept'] = 'application/json'
     if access_token:
         headers['Authorization'] = f'Bearer {access_token}'
 
-    # Allow user agent to be passed either in params or as a separate kwarg
-    if 'user_agent' in params:
-        user_agent = params.pop('user_agent')
-    headers['User-Agent'] = user_agent or pyinaturalist.user_agent
-
     # If one or more resources are requested by ID, valudate and update the request URL accordingly
     if ids:
         url = url.rstrip('/') + '/' + validate_ids(ids)
diff --git a/pyinaturalist/v0/observation_fields.py b/pyinaturalist/v0/observation_fields.py
index d58e74e3..d2dc738b 100644
--- a/pyinaturalist/v0/observation_fields.py
+++ b/pyinaturalist/v0/observation_fields.py
@@ -31,7 +31,7 @@ def get_observation_fields(**params) -> JsonResponse:
     Returns:
         Observation fields as a list of dicts
     """
-    response = get(f'{API_V0_BASE_URL}/observation_fields.json', params=params)
+    response = get(f'{API_V0_BASE_URL}/observation_fields.json', **params)
     obs_fields = response.json()
     obs_fields = convert_all_timestamps(obs_fields)
     return {'results': obs_fields}
@@ -42,7 +42,7 @@ def put_observation_field_values(
     observation_field_id: int,
     value: Any,
     access_token: str,
-    user_agent: str = None,
+    **kwargs,
 ) -> JsonResponse:
     # TODO: Also implement a put_or_update_observation_field_values() that deletes then recreates the field_value?
     # TODO: Return some meaningful exception if it fails because the field is already set.
@@ -79,13 +79,11 @@ def put_observation_field_values(
         observation_field_id: ID of the observation field for this observation field value
         value: Value for the observation field
         access_token: The access token, as returned by :func:`get_access_token()`
-        user_agent: A user-agent string that will be passed to iNaturalist.
 
     Returns:
         The newly updated field value record
     """
-
-    payload = {
+    json_body = {
         'observation_field_value': {
             'observation_id': observation_id,
             'observation_field_id': observation_field_id,
@@ -96,7 +94,7 @@ def put_observation_field_values(
     response = put(
         f'{API_V0_BASE_URL}/observation_field_values/{observation_field_id}',
         access_token=access_token,
-        user_agent=user_agent,
-        json=payload,
+        json=json_body,
+        **kwargs,
     )
     return response.json()
diff --git a/pyinaturalist/v0/observations.py b/pyinaturalist/v0/observations.py
index 71a770e0..49601d4c 100644
--- a/pyinaturalist/v0/observations.py
+++ b/pyinaturalist/v0/observations.py
@@ -90,11 +90,7 @@ def get_observations(**params) -> Union[List, str]:
         raise ValueError('Invalid response format')
     validate_multiple_choice_param(params, 'order_by', REST_OBS_ORDER_BY_PROPERTIES)
 
-    response = get(
-        f'{API_V0_BASE_URL}/observations.{converters}',
-        params=params,
-    )
-
+    response = get(f'{API_V0_BASE_URL}/observations.{converters}', **params)
     if converters == 'json':
         observations = response.json()
         observations = convert_all_coordinates(observations)
@@ -141,11 +137,13 @@ def create_observation(access_token: str, **params) -> ListResponse:
         ``response`` attribute gives more details about the errors.
     """
 
-    params, photos, sounds = _process_observation_params(params)
+    params, photos, sounds, user_agent, session = _process_observation_params(params)
     response = post(
         url=f'{API_V0_BASE_URL}/observations.json',
         json={'observation': params},
         access_token=access_token,
+        user_agent=user_agent,
+        session=session,
     )
     response_json = response.json()
     observation_id = response_json[0]['id']
@@ -165,11 +163,7 @@ def create_observation(access_token: str, **params) -> ListResponse:
         docs._update_observation,
     ]
 )
-def update_observation(
-    observation_id: int,
-    access_token: str,
-    **params,
-) -> ListResponse:
+def update_observation(observation_id: int, access_token: str, **params) -> ListResponse:
     """
     Update a single observation.
 
@@ -204,11 +198,13 @@ def update_observation(
         :py:exc:`requests.HTTPError`, if the call is not successful. iNaturalist returns an
             error 410 if the observation doesn't exists or belongs to another user.
     """
-    params, photos, sounds = _process_observation_params(params)
+    params, photos, sounds, user_agent, session = _process_observation_params(params)
     response = put(
         url=f'{API_V0_BASE_URL}/observations/{observation_id}.json',
         json={'observation': params},
         access_token=access_token,
+        user_agent=user_agent,
+        session=session,
     )
 
     if photos:
@@ -234,15 +230,12 @@ def _process_observation_params(params):
     else:
         params['ignore_photos'] = 1
 
-    return params, photos, sounds
+    user_agent = params.pop('user_agent', None)
+    session = params.pop('session', None)
+    return params, photos, sounds, user_agent, session
 
 
-def upload_photos(
-    observation_id: int,
-    photos: MultiFile,
-    access_token: str,
-    user_agent: str = None,
-) -> ListResponse:
+def upload_photos(observation_id: int, photos: MultiFile, access_token: str, **params) -> ListResponse:
     """Upload a local photo and assign it to an existing observation.
 
     Example:
@@ -268,7 +261,6 @@ def upload_photos(
         observation_id: the ID of the observation
         photo: An image file, file-like object, or path
         access_token: the access token, as returned by :func:`get_access_token()`
-        user_agent: a user-agent string that will be passed to iNaturalist.
 
     Returns:
         Information about the uploaded photo(s)
@@ -279,10 +271,10 @@ def upload_photos(
         response = post(
             url=f'{API_V0_BASE_URL}/observation_photos',
             access_token=access_token,
-            params={'observation_photo[observation_id]': observation_id},
             files={'file': ensure_file_obj(photo)},
-            user_agent=user_agent,
             raise_for_status=False,
+            **{'observation_photo[observation_id]': observation_id},
+            **params,
         )
         responses.append(response)
 
@@ -292,15 +284,8 @@ def upload_photos(
     return [response.json() for response in responses]
 
 
-def upload_sounds(
-    observation_id: int,
-    sounds: MultiFile,
-    access_token: str,
-    user_agent: str = None,
-) -> ListResponse:
-    """Upload a local photo and assign it to an existing observation.
-
-    **API reference:** https://www.inaturalist.org/pages/api+reference#post-observation_photos
+def upload_sounds(observation_id: int, sounds: MultiFile, access_token: str, **params) -> ListResponse:
+    """Upload a local sound file and assign it to an existing observation.
 
     Example:
 
@@ -325,7 +310,6 @@ def upload_sounds(
         observation_id: the ID of the observation
         sound: An audio file, file-like object, or path
         access_token: the access token, as returned by :func:`get_access_token()`
-        user_agent: a user-agent string that will be passed to iNaturalist.
 
     Returns:
         Information about the uploaded sound(s)
@@ -336,10 +320,10 @@ def upload_sounds(
         response = post(
             url=f'{API_V0_BASE_URL}/observation_sounds',
             access_token=access_token,
-            params={'observation_sound[observation_id]': observation_id},
             files={'file': ensure_file_obj(sound)},
-            user_agent=user_agent,
             raise_for_status=False,
+            **{'observation_sound[observation_id]': observation_id},
+            **params,
         )
         responses.append(response)
 
@@ -350,7 +334,7 @@ def upload_sounds(
 
 
 @document_request_params([docs._observation_id, docs._access_token])
-def delete_observation(observation_id: int, access_token: str = None, user_agent: str = None):
+def delete_observation(observation_id: int, access_token: str = None, **params):
     """
     Delete an observation.
 
@@ -371,8 +355,8 @@ def delete_observation(observation_id: int, access_token: str = None, user_agent
     response = delete(
         url=f'{API_V0_BASE_URL}/observations/{observation_id}.json',
         access_token=access_token,
-        user_agent=user_agent,
         raise_for_status=False,
+        **params,
     )
     if response.status_code == 404:
         raise ObservationNotFound
diff --git a/pyinaturalist/v1/controlled_terms.py b/pyinaturalist/v1/controlled_terms.py
index 95e70ec0..b95f0188 100644
--- a/pyinaturalist/v1/controlled_terms.py
+++ b/pyinaturalist/v1/controlled_terms.py
@@ -3,7 +3,7 @@
 from pyinaturalist.v1 import get_v1
 
 
-def get_controlled_terms(taxon_id: int = None, user_agent: str = None) -> JsonResponse:
+def get_controlled_terms(taxon_id: int = None, **params) -> JsonResponse:
     """List controlled terms and their possible values.
     A taxon ID can optionally be provided to show only terms that are valid for that taxon.
     Otherwise, all controlled terms will be returned.
@@ -36,7 +36,6 @@ def get_controlled_terms(taxon_id: int = None, user_agent: str = None) -> JsonRe
                 :language: JSON
     Args:
         taxon_id: ID of taxon to get controlled terms for
-        user_agent: a user-agent string that will be passed to iNaturalist.
 
     Returns:
         A dict containing details on controlled terms and their values
@@ -46,7 +45,7 @@ def get_controlled_terms(taxon_id: int = None, user_agent: str = None) -> JsonRe
     """
     # This is actually two endpoints, but they are so similar it seems best to combine them
     endpoint = 'controlled_terms/for_taxon' if taxon_id else 'controlled_terms'
-    response = get_v1(endpoint, params={'taxon_id': taxon_id}, user_agent=user_agent)
+    response = get_v1(endpoint, params={'taxon_id': taxon_id}, **params)
 
     # controlled_terms/for_taxon returns a 422 if the specified taxon does not exist
     if response.status_code in (404, 422):
diff --git a/pyinaturalist/v1/identifications.py b/pyinaturalist/v1/identifications.py
index f28407b8..73cc8988 100644
--- a/pyinaturalist/v1/identifications.py
+++ b/pyinaturalist/v1/identifications.py
@@ -7,7 +7,7 @@
 from pyinaturalist.v1 import get_v1
 
 
-def get_identifications_by_id(identification_id: MultiInt, user_agent: str = None) -> JsonResponse:
+def get_identifications_by_id(identification_id: MultiInt, **params) -> JsonResponse:
     """Get one or more identification records by ID.
 
     **API reference:** https://api.inaturalist.org/v1/docs/#!/Identifications/get_identifications_id
@@ -27,7 +27,7 @@ def get_identifications_by_id(identification_id: MultiInt, user_agent: str = Non
     Returns:
         Response dict containing identification records
     """
-    response = get_v1('identifications', ids=identification_id, user_agent=user_agent)
+    response = get_v1('identifications', ids=identification_id, **params)
     identifications = response.json()
     identifications['results'] = convert_all_timestamps(identifications['results'])
     return identifications
@@ -60,7 +60,7 @@ def get_identifications(**params) -> JsonResponse:
         Response dict containing identification records
     """
     params = convert_rank_range(params)
-    response = get_v1('identifications', params=params)
+    response = get_v1('identifications', **params)
     identifications = response.json()
     identifications['results'] = convert_all_timestamps(identifications['results'])
     return identifications
diff --git a/pyinaturalist/v1/observations.py b/pyinaturalist/v1/observations.py
index 99bbbaad..0be10940 100644
--- a/pyinaturalist/v1/observations.py
+++ b/pyinaturalist/v1/observations.py
@@ -18,7 +18,7 @@
 from pyinaturalist.v1 import get_v1
 
 
-def get_observation(observation_id: int, user_agent: str = None) -> JsonResponse:
+def get_observation(observation_id: int, **params) -> JsonResponse:
     """Get details about a single observation by ID
 
     **API reference:** https://api.inaturalist.org/v1/docs/#!/Observations/get_observations_id
@@ -35,8 +35,7 @@ def get_observation(observation_id: int, user_agent: str = None) -> JsonResponse
             .. literalinclude:: ../sample_data/get_observation.py
 
     Args:
-        observation_id: Observation ID
-        user_agent: a user-agent string that will be passed to iNaturalist.
+        observation_id: Get the observation with this ID. Only a single value is allowed.
 
     Returns:
         A dict with details on the observation
@@ -45,7 +44,7 @@ def get_observation(observation_id: int, user_agent: str = None) -> JsonResponse
         :py:exc:`.ObservationNotFound` If an invalid observation is specified
     """
 
-    response = get_observations(id=observation_id, user_agent=user_agent)
+    response = get_observations(id=observation_id, **params)
     if response['results']:
         return convert_observation_timestamps(response['results'][0])
     raise ObservationNotFound()
@@ -101,7 +100,7 @@ def get_observation_histogram(**params) -> HistogramResponse:
         Dict of ``{time_key: observation_count}``. Keys are ints for 'month of year' and\
         'week of year' intervals, and :py:class:`~datetime.datetime` objects for all other intervals.
     """
-    response = get_v1('observations/histogram', params=params)
+    response = get_v1('observations/histogram', **params)
     return convert_histogram(response.json())
 
 
@@ -141,7 +140,7 @@ def get_observations(**params) -> JsonResponse:
         Response dict containing observation records
     """
     validate_multiple_choice_param(params, 'order_by', NODE_OBS_ORDER_BY_PROPERTIES)
-    response = get_v1('observations', params=params)
+    response = get_v1('observations', **params)
 
     observations = response.json()
     observations['results'] = convert_all_coordinates(observations['results'])
@@ -175,7 +174,7 @@ def get_observation_species_counts(**params) -> JsonResponse:
     Returns:
         Response dict containing taxon records with counts
     """
-    response = get_v1('observations/species_counts', params=params)
+    response = get_v1('observations/species_counts', **params)
     return response.json()
 
 
@@ -209,7 +208,7 @@ def get_observation_observers(**params) -> JsonResponse:
         Response dict of observers
     """
     params.setdefault('per_page', 500)
-    response = get_v1('observations/observers', params=params)
+    response = get_v1('observations/observers', **params)
     return response.json()
 
 
@@ -239,12 +238,12 @@ def get_observation_identifiers(**params) -> JsonResponse:
         Response dict of identifiers
     """
     params.setdefault('per_page', 500)
-    response = get_v1('observations/identifiers', params=params)
+    response = get_v1('observations/identifiers', **params)
     return response.json()
 
 
 @add_paginate_all(method='page')
-def get_observation_taxonomy(user_id: IntOrStr, user_agent: str = None) -> JsonResponse:
+def get_observation_taxonomy(user_id: IntOrStr, **params) -> JsonResponse:
     """Get observation counts for all taxa in a full taxonomic tree. In the web UI, these are used
     for life lists.
 
@@ -264,5 +263,5 @@ def get_observation_taxonomy(user_id: IntOrStr, user_agent: str = None) -> JsonR
     Returns:
         Response dict containing taxon records with counts
     """
-    response = get_v1('observations/taxonomy', params={'user_id': user_id}, user_agent=user_agent)
+    response = get_v1('observations/taxonomy', user_id=user_id, **params)
     return response.json()
diff --git a/pyinaturalist/v1/places.py b/pyinaturalist/v1/places.py
index 7e2c2d1e..19bab8b1 100644
--- a/pyinaturalist/v1/places.py
+++ b/pyinaturalist/v1/places.py
@@ -6,7 +6,7 @@
 from pyinaturalist.v1 import get_v1
 
 
-def get_places_by_id(place_id: MultiInt, user_agent: str = None) -> JsonResponse:
+def get_places_by_id(place_id: MultiInt, **params) -> JsonResponse:
     """
     Get one or more places by ID.
 
@@ -29,7 +29,7 @@ def get_places_by_id(place_id: MultiInt, user_agent: str = None) -> JsonResponse
     Returns:
         Response dict containing place records
     """
-    response = get_v1('places', ids=place_id, user_agent=user_agent)
+    response = get_v1('places', ids=place_id, **params)
 
     # Convert coordinates to floats
     places = response.json()
@@ -71,7 +71,7 @@ def get_places_nearby(**params) -> JsonResponse:
     Returns:
         Response dict containing place records, divided into 'standard' and 'community' places.
     """
-    response = get_v1('places/nearby', params=params)
+    response = get_v1('places/nearby', **params)
     return convert_all_place_coordinates(response.json())
 
 
@@ -99,13 +99,10 @@ def get_places_autocomplete(q: str = None, **params) -> JsonResponse:
 
             .. literalinclude:: ../sample_data/get_places_autocomplete.py
 
-    Args:
-        q: Name must begin with this value
-
     Returns:
         Response dict containing place records
     """
-    response = get_v1('places/autocomplete', params={'q': q, **params})
+    response = get_v1('places/autocomplete', q=q, **params)
 
     # Convert coordinates to floats
     places = response.json()
diff --git a/pyinaturalist/v1/projects.py b/pyinaturalist/v1/projects.py
index 027dfbfe..71ccdcf0 100644
--- a/pyinaturalist/v1/projects.py
+++ b/pyinaturalist/v1/projects.py
@@ -44,7 +44,7 @@ def get_projects(**params) -> JsonResponse:
         Response dict containing project records
     """
     validate_multiple_choice_param(params, 'order_by', PROJECT_ORDER_BY_PROPERTIES)
-    response = get_v1('projects', params=params)
+    response = get_v1('projects', **params)
 
     projects = response.json()
     projects['results'] = convert_all_coordinates(projects['results'])
@@ -52,9 +52,7 @@ def get_projects(**params) -> JsonResponse:
     return projects
 
 
-def get_projects_by_id(
-    project_id: MultiInt, rule_details: bool = None, user_agent: str = None
-) -> JsonResponse:
+def get_projects_by_id(project_id: MultiInt, rule_details: bool = None, **params) -> JsonResponse:
     """Get one or more projects by ID.
 
     **API reference:** https://api.inaturalist.org/v1/docs/#!/Projects/get_projects_id
@@ -79,12 +77,7 @@ def get_projects_by_id(
     Returns:
         Response dict containing project records
     """
-    response = get_v1(
-        'projects',
-        ids=project_id,
-        params={'rule_details': rule_details},
-        user_agent=user_agent,
-    )
+    response = get_v1('projects', ids=project_id, params={'rule_details': rule_details}, **params)
 
     projects = response.json()
     projects['results'] = convert_all_coordinates(projects['results'])
diff --git a/pyinaturalist/v1/search.py b/pyinaturalist/v1/search.py
index c72c3add..c5cb6ef0 100644
--- a/pyinaturalist/v1/search.py
+++ b/pyinaturalist/v1/search.py
@@ -29,7 +29,7 @@ def search(q: str, **params) -> JsonResponse:
     Returns:
         Response dict containing search results
     """
-    response = get_v1('search', params={'q': q, **params})
+    response = get_v1('search', q=q, **params)
     search_results = response.json()
     search_results['results'] = convert_all_timestamps(search_results['results'])
     search_results['results'] = convert_all_coordinates(search_results['results'])
diff --git a/pyinaturalist/v1/taxa.py b/pyinaturalist/v1/taxa.py
index ccc92e2d..a6de8156 100644
--- a/pyinaturalist/v1/taxa.py
+++ b/pyinaturalist/v1/taxa.py
@@ -33,13 +33,13 @@ def get_taxa(**params) -> JsonResponse:
         Response dict containing taxon records
     """
     params = convert_rank_range(params)
-    response = get_v1('taxa', params=params)
+    response = get_v1('taxa', **params)
     taxa = response.json()
     taxa['results'] = convert_all_timestamps(taxa['results'])
     return taxa
 
 
-def get_taxa_by_id(taxon_id: MultiInt, user_agent: str = None) -> JsonResponse:
+def get_taxa_by_id(taxon_id: MultiInt, **params) -> JsonResponse:
     """Get one or more taxa by ID.
 
     **API reference:** https://api.inaturalist.org/v1/docs/#!/Taxa/get_taxa_id
@@ -67,7 +67,7 @@ def get_taxa_by_id(taxon_id: MultiInt, user_agent: str = None) -> JsonResponse:
     Returns:
         Response dict containing taxon records
     """
-    response = get_v1('taxa', ids=taxon_id, user_agent=user_agent)
+    response = get_v1('taxa', ids=taxon_id, **params)
     taxa = response.json()
     taxa['results'] = convert_all_timestamps(taxa['results'])
     return taxa
@@ -121,5 +121,5 @@ def get_taxa_autocomplete(**params) -> JsonResponse:
         Response dict containing taxon records
     """
     params = convert_rank_range(params)
-    response = get_v1('taxa/autocomplete', params=params)
+    response = get_v1('taxa/autocomplete', **params)
     return response.json()
diff --git a/pyinaturalist/v1/users.py b/pyinaturalist/v1/users.py
index 287561b0..0a434f0d 100644
--- a/pyinaturalist/v1/users.py
+++ b/pyinaturalist/v1/users.py
@@ -9,7 +9,7 @@
 logger = getLogger(__name__)
 
 
-def get_user_by_id(user_id: int, user_agent: str = None) -> JsonResponse:
+def get_user_by_id(user_id: int, **params) -> JsonResponse:
     """Get a user by ID.
 
     **API reference:** https://api.inaturalist.org/v1/docs/#!/Users/get_users_id
@@ -31,7 +31,7 @@ def get_user_by_id(user_id: int, user_agent: str = None) -> JsonResponse:
     Returns:
         Response dict containing user record
     """
-    response = get_v1('users', ids=[user_id], user_agent=user_agent)
+    response = get_v1('users', ids=[user_id], **params)
     results = response.json()['results']
     if not results:
         return {}
@@ -61,7 +61,7 @@ def get_users_autocomplete(q: str, **params) -> JsonResponse:
     Returns:
         Response dict containing user records
     """
-    response = get_v1('users/autocomplete', params={'q': q, **params})
+    response = get_v1('users/autocomplete', q=q, **params)
     users = response.json()
     users['results'] = convert_all_timestamps(users['results'])
     return users
diff --git a/test/test_api_requests.py b/test/test_api_requests.py
index e3a78aa9..2428d32b 100644
--- a/test/test_api_requests.py
+++ b/test/test_api_requests.py
@@ -13,9 +13,9 @@
     'http_func, http_method',
     [(delete, 'DELETE'), (get, 'GET'), (post, 'POST'), (put, 'PUT')],
 )
-@patch('pyinaturalist.api_requests.requests.Session.request')
+@patch('pyinaturalist.api_requests.Session.request')
 def test_http_methods(mock_request, http_func, http_method):
-    http_func('https://url', params={'key': 'value'})
+    http_func('https://url', key='value', session=None)
     mock_request.assert_called_with(
         http_method,
         'https://url',
@@ -45,13 +45,21 @@ def test_http_methods(mock_request, http_func, http_method):
         ),
     ],
 )
-@patch('pyinaturalist.api_requests.requests.Session.request')
+@patch('pyinaturalist.api_requests.Session.request')
 def test_request_headers(mock_request, input_kwargs, expected_headers):
     request('GET', 'https://url', **input_kwargs)
     request_kwargs = mock_request.call_args[1]
     assert request_kwargs['headers'] == expected_headers
 
 
+@patch('pyinaturalist.api_requests.get_session')
+def test_request_session(mock_get_session):
+    mock_session = MagicMock()
+    request('GET', 'https://url', session=mock_session)
+    mock_session.request.assert_called()
+    mock_get_session.assert_not_called()
+
+
 # Test relevant combinations of dry-run settings and HTTP methods
 @pytest.mark.parametrize(
     'enabled_const, enabled_env, write_only_const, write_only_env, method, expected_real_request',
@@ -85,7 +93,7 @@ def test_request_headers(mock_request, input_kwargs, expected_headers):
     ],
 )
 @patch('pyinaturalist.api_requests.getenv')
-@patch('pyinaturalist.api_requests.requests.Session.request')
+@patch('pyinaturalist.api_requests.Session.request')
 def test_request_dry_run(
     mock_request,
     mock_getenv,
diff --git a/test/v1/test_taxa.py b/test/v1/test_taxa.py
index e6384159..842e13b1 100644
--- a/test/v1/test_taxa.py
+++ b/test/v1/test_taxa.py
@@ -49,17 +49,17 @@ def test_get_taxa_by_rank_range(
 ):
     # Make sure custom rank params result in the correct 'rank' param value
     get_taxa(**params)
-    kwargs = mock_get.call_args[1]
-    requested_rank = kwargs['params']['rank']
+    params = mock_get.call_args[1]
+    requested_rank = params['rank']
     assert requested_rank == expected_ranks
 
 
 # This is just a spot test of a case in which boolean params should be converted
-@patch('pyinaturalist.api_requests.requests.Session.request')
+@patch('pyinaturalist.api_requests.Session.request')
 def test_get_taxa_by_name_and_is_active(request):
     get_taxa(q='Lixus bardanae', is_active=False)
-    request_kwargs = request.call_args[1]
-    assert request_kwargs['params'] == {'q': 'Lixus bardanae', 'is_active': 'false'}
+    params = request.call_args[1]['params']
+    assert params['q'] == 'Lixus bardanae' and params['is_active'] == 'false'
 
 
 def test_get_taxa_by_id(requests_mock):