diff --git a/README.rst b/README.rst
index 2a530b7..ec87739 100644
--- a/README.rst
+++ b/README.rst
@@ -36,7 +36,7 @@ The ``read_data`` function expects the following arguments:
         "2026-01-02"
     )
 
-You can optionally specify an API key for instances that require one.
+You can specify an API key for instances that require one.
 
 .. code:: python
 
@@ -48,6 +48,19 @@ You can optionally specify an API key for instances that require one.
         api_key="<api key>"
     )
 
+You can specify a username and password for instances that require basic auth.
+
+.. code:: python
+
+   df = read_data(
+        "https://lasp.colorado.edu/lisird/latis/dap2",
+        "bremen_composite_mgii",
+        "2026-01-01",
+        "2026-01-02",
+        username="<username>",
+        password="<password>"
+    )
+
 For queries more complicated than time selections, you can optionally specify an additional `DAP2 query fragment <https://lasp.colorado.edu/lisird/about/latis>`__ that will be appended to the query sent to LaTiS. It must be URL-encoded.
 
 .. code:: python
diff --git a/src/latis/client.py b/src/latis/client.py
index cd3013a..6c607f0 100644
--- a/src/latis/client.py
+++ b/src/latis/client.py
@@ -9,12 +9,15 @@
 import numpy as np
 import pandas as pd
 import requests
+from requests.auth import AuthBase
+from requests.auth import HTTPBasicAuth
 import urllib.parse
 from typing import List, Dict, Any, Union, Optional
 
 
-def read_data(base_url, dataset, start_time, end_time,
-              api_key=None, api_key_header="x-api-key", query=None):
+def read_data(base_url, dataset, start_time, end_time, api_key=None,
+              api_key_header="x-api-key", username=None, password=None,
+              query=None):
     """
     Make a request to a LaTiS instance for data.
 
@@ -31,6 +34,10 @@ def read_data(base_url, dataset, start_time, end_time,
         api_key (str): If set, the API key sent with the request.
         api_key_header (str): The HTTP header used to include the API
           key given by ``api_key``.
+        username (str): If set, the username used for basic auth when
+          making the request.
+        password (str): If set, the password used for basic auth when
+          making the request.
         query (str): Optional additional OPeNDAP DAP2 query fragment.
           Must be URL-encoded.
 
@@ -49,17 +56,21 @@ def read_data(base_url, dataset, start_time, end_time,
         rest="" if query is None else "&" + query
     )
 
-    headers = {}
+    # No auth by default.
+    auth = None
+
     if api_key is not None:
-        headers[api_key_header] = api_key
+        auth = APIKeyAuth(api_key, api_key_header)
+    elif username is not None and password is not None:
+        auth = HTTPBasicAuth(username, password)
 
     # If dataset is a string, make a DAP2 query. If dataset is a list
     # or a tuple, make a join query.
     if isinstance(dataset, str):
-        res = _make_dap2_query(base_url, dataset, query, headers)
+        res = _make_dap2_query(base_url, dataset, query, auth)
     elif isinstance(dataset, (list, tuple)):
         if len(dataset) == 1:
-            res = _make_dap2_query(base_url, dataset[0], query, headers)
+            res = _make_dap2_query(base_url, dataset[0], query, auth)
         else:
             # Joining is only supported for LaTiS 3 instances. The
             # only way we can check whether an instance is a LaTiS 3
@@ -74,7 +85,7 @@ def read_data(base_url, dataset, start_time, end_time,
                 # slash.
                 join_url = base_url.rstrip("/dap2") + "/join"
 
-                res = _make_join_query(join_url, dataset, query, headers)
+                res = _make_join_query(join_url, dataset, query, auth)
             else:
                 # Probably not a LaTiS 3 instance.
                 raise ValueError(
@@ -95,7 +106,7 @@ def read_data(base_url, dataset, start_time, end_time,
     return df
 
 
-def _make_dap2_query(base, dataset, query, headers):
+def _make_dap2_query(base, dataset, query, auth):
     """
     Makes a DAP 2 request to a LaTiS instance.
     """
@@ -106,11 +117,11 @@ def _make_dap2_query(base, dataset, query, headers):
         query=query
     )
 
-    res = requests.get(url, headers=headers)
+    res = requests.get(url, auth=auth)
     return res
 
 
-def _make_join_query(base, datasets, query, headers):
+def _make_join_query(base, datasets, query, auth):
     """
     Makes a request to the join service of a LaTiS 3 instance.
     """
@@ -118,10 +129,33 @@ def _make_join_query(base, datasets, query, headers):
     url = "{base}?{query}".format(base=base, query=query)
     body = {"datasets": datasets}
 
-    res = requests.post(url, json=body, headers=headers)
+    res = requests.post(url, json=body, auth=auth)
     return res
 
 
+class APIKeyAuth(AuthBase):
+    """Authentication using an API key passed in an HTTP header."""
+
+    def __init__(self, key, header='x-api-key'):
+        """
+        Construct an APIKeyAuth instance.
+
+        Args:
+            key (str): The API key
+            header (str): The HTTP header used to pass the API key.
+              Defaults to ``x-api-key``.
+
+        Returns:
+            An APIKeyAuth instance.
+        """
+        self.key = key
+        self.header = header
+
+    def __call__(self, req):
+        req.headers[self.header] = self.key
+        return req
+
+
 class LatisInstance:
     """Represents a LaTiS instance.