diff --git a/README.md b/README.md
index fe48e99..529e824 100644
--- a/README.md
+++ b/README.md
@@ -111,3 +111,25 @@ Actions](https://github.com/nasa/harmony-py/actions) to run the Linter
 ## Building and Releasing
 
 New versions of Harmony-Py will be published to PyPi via a GitHub [action](.github/workflows/publish-release.yml) whenever a draft release is marked as published https://github.com/nasa/harmony-py/releases.
+
+### Download timeouts
+
+File downloads can be given a socket timeout when creating the client:
+
+```python
+client = Client(download_timeout=(10, 60))
+future = client.download(url, directory="downloads", overwrite=True)
+filename = future.result()
+```
+
+The first value limits connection attempts; the second limits how long a socket
+read waits for data. These limits also apply to `download_all` and
+`download_intermediate_files`, including OPeNDAP downloads. A single number sets
+both limits. The default, `None`, retains the existing unlimited wait behavior.
+
+These are inactivity limits, not a deadline for completing a whole file or job.
+Existing request retries may extend the total elapsed time. A download timeout
+is raised through `Future.result()` and releases the download worker. In contrast,
+`Future.result(timeout=...)` only limits the caller's wait and does not interrupt
+the running download. Failed transfers may leave a partial local file; use
+`overwrite=True` when retrying, or remove the incomplete file first.
diff --git a/harmony/client.py b/harmony/client.py
index 0da56e6..fb06dec 100644
--- a/harmony/client.py
+++ b/harmony/client.py
@@ -178,18 +178,25 @@ def __init__(
         token: str | None = None,
         # How often to poll Harmony for updated information during job processing
         check_interval: float = 3.0,  # in seconds
+        download_timeout: float | tuple[float | None, float | None] | None = None,
     ):
         """Creates a Harmony Client that can be used to interact with Harmony.
 
         Args:
             auth : A tuple of the format ('edl_username', 'edl_password')
             should_validate_auth: Whether EDL credentials will be validated.
+            download_timeout: Optional socket timeout for file downloads, in seconds.
+                A number applies to both connection and read timeouts; a tuple supplies
+                separate (connect, read) values. None preserves unlimited waits. Read
+                timeouts limit inactivity, not total download duration, and retries may
+                extend the total elapsed time. Job polling and authentication are unaffected.
         """
         self.config = Config(env)
         self.session = None
         self.auth = auth
         self.token = token
         self.check_interval = check_interval
+        self.download_timeout = download_timeout
 
         num_workers = int(self.config.NUM_REQUESTS_WORKERS)
         self.executor = ThreadPoolExecutor(max_workers=num_workers)
@@ -969,7 +976,11 @@ def _download_file(self, url: str, directory: str = '', overwrite: bool = False)
                 data_dict = dict(parse.parse_qsl(parse.urlsplit(url).query))
             headers = {'Accept-Encoding': 'identity'}
             with getattr(session, method)(
-                new_url, data=data_dict, stream=True, headers=headers
+                new_url,
+                data=data_dict,
+                stream=True,
+                headers=headers,
+                timeout=self.download_timeout,
             ) as r:
                 # Without this an error response body (a 401 page, a Harmony
                 # error document) is written to disk and looks like data.
diff --git a/tests/test_download_timeout.py b/tests/test_download_timeout.py
new file mode 100644
index 0000000..0a37dbc
--- /dev/null
+++ b/tests/test_download_timeout.py
@@ -0,0 +1,161 @@
+"""Offline coverage for download connection and read timeouts."""
+
+from contextlib import contextmanager
+from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
+from threading import Event, Thread
+from unittest.mock import MagicMock
+import io
+
+import pytest
+import requests
+from urllib3.exceptions import ReadTimeoutError
+
+from harmony.client import Client
+
+
+@pytest.mark.parametrize('timeout', [None, 10, (2, 30), (2, None)])
+@pytest.mark.parametrize('opendap', [False, True])
+def test_download_timeout_reaches_request(tmp_path, timeout, opendap):
+    client = Client(should_validate_auth=False, download_timeout=timeout)
+    session = MagicMock()
+    client.session = session
+    response = MagicMock()
+    response.raw = io.BytesIO(b'data')
+    response.__enter__.return_value = response
+    method = session.post if opendap else session.get
+    method.return_value = response
+    url = 'https://opendap.example/data.nc?dap4.ce=x' if opendap else 'https://example/data.nc'
+    try:
+        result = client.download(url, directory=str(tmp_path)).result(timeout=5)
+        assert method.call_args.kwargs['timeout'] == timeout
+        assert method.call_args.kwargs['headers'] == {'Accept-Encoding': 'identity'}
+        assert method.call_args.kwargs['stream'] is True
+        assert method.call_args.kwargs['data'] == ({'dap4.ce': 'x'} if opendap else None)
+        assert (tmp_path / 'data.nc').read_bytes() == b'data'
+        assert result == str(tmp_path / 'data.nc')
+        response.raise_for_status.assert_called_once()
+        response.__exit__.assert_called_once()
+    finally:
+        client.executor.shutdown(wait=True)
+
+
+@pytest.mark.parametrize('timeout', [None, (2, 30)])
+def test_existing_download_is_not_requested(tmp_path, timeout):
+    (tmp_path / 'data.nc').write_bytes(b'existing')
+    client = Client(should_validate_auth=False, download_timeout=timeout)
+    client.session = MagicMock()
+    try:
+        result = client.download('https://example/data.nc', str(tmp_path)).result(timeout=5)
+        assert result == str(tmp_path / 'data.nc')
+        client.session.get.assert_not_called()
+        assert (tmp_path / 'data.nc').read_bytes() == b'existing'
+    finally:
+        client.executor.shutdown(wait=True)
+
+
+def test_connect_timeout_reaches_future(tmp_path):
+    client = Client(should_validate_auth=False, download_timeout=(1, 3))
+    client.session = MagicMock()
+    client.session.get.side_effect = requests.exceptions.ConnectTimeout('connection stalled')
+    try:
+        future = client.download('https://example/data.nc', str(tmp_path))
+        with pytest.raises(requests.exceptions.ConnectTimeout):
+            future.result(timeout=5)
+        assert not (tmp_path / 'data.nc').exists()
+    finally:
+        client.executor.shutdown(wait=True)
+
+
+@contextmanager
+def stalled_server(send_headers):
+    """Release blocked handlers before cleanup, even when a timeout regression fails."""
+    release = Event()
+    entered = Event()
+
+    class Handler(BaseHTTPRequestHandler):
+        def do_GET(self):
+            if send_headers:
+                self.send_response(200)
+                self.send_header('Content-Length', '10')
+                self.end_headers()
+                self.wfile.write(b'part')
+                self.wfile.flush()
+            entered.set()
+            release.wait(timeout=10)
+
+        def log_message(self, *args):
+            pass
+
+    server = ThreadingHTTPServer(('127.0.0.1', 0), Handler)
+    thread = Thread(target=server.serve_forever, daemon=True)
+    thread.start()
+    try:
+        yield f'http://127.0.0.1:{server.server_port}/data.nc', entered
+    finally:
+        release.set()
+        server.shutdown()
+        server.server_close()
+        thread.join(timeout=5)
+
+
+@pytest.mark.parametrize('send_headers', [False, True])
+def test_stalled_download_releases_worker(tmp_path, send_headers, monkeypatch):
+    monkeypatch.setenv('NUM_REQUESTS_WORKERS', '1')
+    client = Client(should_validate_auth=False, download_timeout=(0.2, 0.2))
+    client.session = requests.Session()
+    client.session.trust_env = False
+    try:
+        with stalled_server(send_headers) as (url, entered):
+            future = client.download(url, str(tmp_path))
+            assert entered.wait(timeout=5)
+            # Requests handles the response headers; urllib3 reads the streamed raw body.
+            with pytest.raises((requests.exceptions.ReadTimeout, ReadTimeoutError)):
+                future.result(timeout=5)
+            assert client.executor.submit(lambda: 'available').result(timeout=5) == 'available'
+    finally:
+        client.session.close()
+        client.executor.shutdown(wait=True)
+
+
+@pytest.mark.parametrize('entry_point', ['job', 'results', 'intermediate'])
+def test_bulk_downloads_use_client_timeout(tmp_path, entry_point, monkeypatch):
+    client = Client(should_validate_auth=False, download_timeout=(2, 30))
+    client.session = MagicMock()
+    response = MagicMock()
+    response.__enter__.return_value = response
+    response.raw = io.BytesIO(b'data')
+    client.session.get.return_value = response
+    url = 'https://example/data.nc'
+    try:
+        if entry_point == 'job':
+            monkeypatch.setattr(client, 'result_urls', lambda *args, **kwargs: iter([url]))
+            downloads = client.download_all('job-id', str(tmp_path))
+        elif entry_point == 'results':
+            downloads = client.download_all(
+                {'links': [{'rel': 'data', 'href': url}]}, str(tmp_path)
+            )
+        else:
+            monkeypatch.setattr(
+                client,
+                'submit',
+                lambda _: {
+                    'steps': [{'workItems': [{'inputFiles': [url], 'outputFiles': []}]}],
+                },
+            )
+            downloads = client.download_intermediate_files('job-id', [1], directory=str(tmp_path))
+        assert [future.result(timeout=5) for future in downloads] == [str(tmp_path / 'data.nc')]
+        assert client.session.get.call_args.kwargs['timeout'] == (2, 30)
+    finally:
+        client.executor.shutdown(wait=True)
+
+
+def test_default_retains_unlimited_waits(tmp_path):
+    client = Client(should_validate_auth=False)
+    client.session = MagicMock()
+    response = client.session.get.return_value.__enter__.return_value
+    response.raw = io.BytesIO(b'data')
+    try:
+        client.download('https://example/data.nc', str(tmp_path)).result(timeout=5)
+        assert client.session.get.call_args.kwargs['timeout'] is None
+    finally:
+        client.executor.shutdown(wait=True)