diff --git a/cmr/queries.py b/cmr/queries.py
index cdf9f2e..3698f10 100644
--- a/cmr/queries.py
+++ b/cmr/queries.py
@@ -5,6 +5,7 @@
 from abc import abstractmethod
 from collections import defaultdict
 from datetime import date, datetime, timezone
+from importlib.metadata import version as _pkg_version
 from inspect import getmembers, ismethod
 from re import search
 from typing import Iterator
@@ -39,6 +40,19 @@
 PointLike: TypeAlias = Tuple[FloatLike, FloatLike]
 
 
+def _format_float(value: float) -> str:
+    """Format a float as a plain decimal string, never using scientific notation.
+
+    Python's default str() and f-strings switch to scientific notation for numbers
+    outside roughly [1e-4, 1e16), e.g. ``1e-05`` for ``0.00001``.  CMR rejects
+    scientific notation in URL parameters with "is not a valid URL encoded point".
+    """
+    formatted = f"{value:.15g}"
+    if "e" in formatted or "E" in formatted:
+        formatted = f"{value:.15f}".rstrip("0").rstrip(".")
+    return formatted
+
+
 class Query:
     """
     Base class for all CMR queries.
@@ -365,6 +379,34 @@ def bearer_token(self, bearer_token: str) -> Self:
 
         return self
 
+    def client_id(self, client_id: Optional[str] = None) -> Self:
+        """
+        Set the ``Client-Id`` header to identify this client to the CMR API.
+
+        If no *client_id* is provided (or ``None`` is passed), a default value
+        of ``python_cmr-<version>`` is used so that NASA Operations can track
+        queries by library version.
+
+        :param client_id: an optional human-readable identifier for your
+            application.  When supplied, the string is suffixed with the
+            library version: ``<client_id>/python_cmr-<version>``.
+        :returns: self
+        """
+
+        try:
+            lib_version = _pkg_version("python-cmr")
+        except Exception:
+            lib_version = "unknown"
+
+        if client_id:
+            header_value = f"{client_id}/python_cmr-{lib_version}"
+        else:
+            header_value = f"python_cmr-{lib_version}"
+
+        self.headers.update({"Client-Id": header_value})
+
+        return self
+
     def option(
         self, parameter: str, key: str, value: Union[str, bool, int, float, None]
     ) -> Self:
@@ -618,7 +660,7 @@ def point(self, lon: FloatLike, lat: FloatLike) -> Self:
         if "point" not in self.params:
             self.params["point"] = []
 
-        self.params["point"].append(f"{lon},{lat}")
+        self.params["point"].append(f"{_format_float(lon)},{_format_float(lat)}")
 
         return self
 
@@ -630,7 +672,7 @@ def circle(self, lon: FloatLike, lat: FloatLike, dist: FloatLike) -> Self:
         :param dist: distance in meters around waypoint (lat,lon)
         :returns: self
         """
-        self.params['circle'] = f"{lon},{lat},{dist}"
+        self.params['circle'] = f"{_format_float(lon)},{_format_float(lat)},{_format_float(float(dist))}"
 
         return self
 
@@ -672,7 +714,7 @@ def polygon(self, coordinates: Sequence[PointLike]) -> Self:
             )
 
         # convert to strings
-        as_strs = [str(val) for val in as_floats]
+        as_strs = [_format_float(val) for val in as_floats]
 
         self.params["polygon"] = ",".join(as_strs)
 
@@ -697,7 +739,8 @@ def bounding_box(
         """
 
         self.params["bounding_box"] = (
-            f"{float(lower_left_lon)},{float(lower_left_lat)},{float(upper_right_lon)},{float(upper_right_lat)}"
+            f"{_format_float(float(lower_left_lon))},{_format_float(float(lower_left_lat))},"
+            f"{_format_float(float(upper_right_lon))},{_format_float(float(upper_right_lat))}"
         )
 
         return self
@@ -734,7 +777,7 @@ def line(self, coordinates: Sequence[PointLike]) -> Self:
             as_floats.extend([float(lon), float(lat)])
 
         # cast back to string for join
-        as_strs = [str(val) for val in as_floats]
+        as_strs = [_format_float(val) for val in as_floats]
 
         self.params["line"] = ",".join(as_strs)
 
@@ -774,18 +817,25 @@ def entry_title(self, entry_title: str) -> Self:
 
         return self
 
-    def platform(self, platform: str) -> Self:
+    def platform(self, platform: Union[str, Sequence[str]]) -> Self:
         """
         Filter by the satellite platform the granule came from.
 
-        :param platform: name of the satellite
+        Accepts either a single platform name or a list of platform names.
+        When multiple platforms are provided, CMR returns results matching
+        any of them.
+
+        :param platform: name of the satellite, or a list of satellite names
         :returns: self
         """
 
         if not platform:
             raise ValueError("Please provide a value for platform")
 
-        self.params['platform'] = platform
+        if isinstance(platform, str):
+            platform = [platform]
+
+        self.params['platform'] = list(platform)
         return self
 
 
diff --git a/tests/test_collection.py b/tests/test_collection.py
index 2c2d866..b26fa93 100644
--- a/tests/test_collection.py
+++ b/tests/test_collection.py
@@ -142,7 +142,15 @@ def test_platform(self):
         query.platform("1B")
 
         self.assertIn("platform", query.params)
-        self.assertEqual(query.params["platform"], "1B")
+        self.assertEqual(query.params["platform"], ["1B"])
+
+    def test_platform_multiple(self):
+        query = CollectionQuery()
+
+        query.platform(["Terra", "Aqua"])
+
+        self.assertIn("platform", query.params)
+        self.assertEqual(query.params["platform"], ["Terra", "Aqua"])
 
     def test_empty_platform(self):
         query = CollectionQuery()
diff --git a/tests/test_granule.py b/tests/test_granule.py
index fbf188f..6c92e52 100644
--- a/tests/test_granule.py
+++ b/tests/test_granule.py
@@ -342,7 +342,15 @@ def test_platform(self):
         query.platform("1B")
 
         self.assertIn(self.platform, query.params)
-        self.assertEqual(query.params[self.platform], "1B")
+        self.assertEqual(query.params[self.platform], ["1B"])
+
+    def test_platform_multiple(self):
+        query = GranuleQuery()
+
+        query.platform(["Terra", "Aqua"])
+
+        self.assertIn(self.platform, query.params)
+        self.assertEqual(query.params[self.platform], ["Terra", "Aqua"])
 
     def test_sort_key(self):
         query = GranuleQuery()
diff --git a/tests/test_queries.py b/tests/test_queries.py
index 142a026..30a25bd 100644
--- a/tests/test_queries.py
+++ b/tests/test_queries.py
@@ -55,3 +55,28 @@ def test_token_replaces_existing_auth_header():
     query.token("token")
 
     assert query.headers["Authorization"] == "token"
+
+
+def test_client_id_default_uses_library_version():
+    query = MockQuery("/foo")
+    query.client_id()
+
+    assert "Client-Id" in query.headers
+    assert query.headers["Client-Id"].startswith("python_cmr-")
+
+
+def test_client_id_custom_includes_app_name_and_version():
+    query = MockQuery("/foo")
+    query.client_id("my-app")
+
+    assert "Client-Id" in query.headers
+    assert query.headers["Client-Id"].startswith("my-app/python_cmr-")
+
+
+def test_client_id_does_not_clobber_other_headers():
+    query = MockQuery("/foo")
+    query.headers["Authorization"] = "Bearer token"
+    query.client_id("my-app")
+
+    assert query.headers["Authorization"] == "Bearer token"
+    assert "Client-Id" in query.headers