diff --git a/resend/_path.py b/resend/_path.py
new file mode 100644
index 0000000..c077e4f
--- /dev/null
+++ b/resend/_path.py
@@ -0,0 +1,18 @@
+import re
+
+_DOT_SEGMENT = re.compile(r"^(?:\.|%2e){1,2}$", re.IGNORECASE)
+
+
+def has_dot_segment(path: str) -> bool:
+    """Whether a request path contains a `.` or `..` segment.
+
+    HTTP clients resolve these before sending (requests/urllib3 and httpx both
+    do), so an id such as "../api-keys/key_id" would reach another endpoint.
+    """
+    pathname = re.split(r"[?#]", path, maxsplit=1)[0]
+    return any(_DOT_SEGMENT.match(segment) for segment in pathname.split("/"))
+
+
+def ensure_no_dot_segments(path: str) -> None:
+    if has_dot_segment(path):
+        raise ValueError("Path parameters cannot be `.` or `..`.")
diff --git a/resend/async_request.py b/resend/async_request.py
index be17658..e791e65 100644
--- a/resend/async_request.py
+++ b/resend/async_request.py
@@ -4,6 +4,7 @@
 from typing_extensions import Literal, TypeVar
 
 import resend
+from resend._path import ensure_no_dot_segments
 from resend.exceptions import (NoContentError, ResendError,
                                raise_for_code_and_type)
 from resend.http_client_async import AsyncHTTPClient
@@ -37,6 +38,7 @@ def __init__(
         self._response_status_code: Optional[int] = None
 
     async def perform(self) -> Union[T, None]:
+        ensure_no_dot_segments(self.path)
         data = await self.make_request(url=f"{resend.api_url}{self.path}")
 
         body_status_code = data.get("statusCode") if isinstance(data, dict) else None
diff --git a/resend/request.py b/resend/request.py
index 56d27c1..92f1d65 100644
--- a/resend/request.py
+++ b/resend/request.py
@@ -4,6 +4,7 @@
 from typing_extensions import Literal, TypeVar
 
 import resend
+from resend._path import ensure_no_dot_segments
 from resend.exceptions import (NoContentError, ResendError,
                                raise_for_code_and_type)
 from resend.response import ResponseDict
@@ -36,6 +37,7 @@ def __init__(
         self._response_status_code: Optional[int] = None
 
     def perform(self) -> Union[T, None]:
+        ensure_no_dot_segments(self.path)
         data = self.make_request(url=f"{resend.api_url}{self.path}")
 
         body_status_code = data.get("statusCode") if isinstance(data, dict) else None
diff --git a/tests/dot_segment_path_test.py b/tests/dot_segment_path_test.py
new file mode 100644
index 0000000..5643164
--- /dev/null
+++ b/tests/dot_segment_path_test.py
@@ -0,0 +1,96 @@
+from typing import Any, Callable, cast
+from unittest.mock import AsyncMock, create_autospec
+
+import pytest
+
+import resend
+from resend._path import has_dot_segment
+from resend.http_client import HTTPClient
+from resend.http_client_async import AsyncHTTPClient
+
+# flake8: noqa
+
+DOT_SEGMENT_CALLS = [
+    lambda: resend.Emails.get(".."),
+    lambda: resend.Emails.cancel(".."),
+    lambda: resend.Domains.remove("."),
+    lambda: resend.Domains.remove("../api-keys/key_id"),
+    lambda: resend.Domains.get("%2E%2E"),
+]
+
+
+@pytest.fixture
+def mock_client() -> Any:
+    resend.api_key = "re_test"
+    previous = resend.default_http_client
+    client = create_autospec(HTTPClient, instance=True)
+    client.request.return_value = (b"{}", 200, {"Content-Type": "application/json"})
+    resend.default_http_client = client
+    yield client
+    resend.default_http_client = previous
+
+
+@pytest.mark.parametrize("call", DOT_SEGMENT_CALLS)
+def test_dot_segment_ids_are_rejected_before_sending(
+    mock_client: Any, call: Callable[[], Any]
+) -> None:
+    with pytest.raises(ValueError, match="cannot be `.` or `..`"):
+        call()
+    mock_client.request.assert_not_called()
+
+
+def test_dotted_ids_are_still_sent(mock_client: Any) -> None:
+    resend.Domains.get("example.com")
+    resend.Contacts.get(email="john.doe@example.com")
+    resend.Domains.get("...")
+    urls = [c.kwargs["url"] for c in mock_client.request.call_args_list]
+    assert urls[0].endswith("/domains/example.com")
+    assert urls[1].endswith("/contacts/john.doe%40example.com")
+    assert urls[2].endswith("/domains/...")
+
+
+@pytest.mark.asyncio
+async def test_dot_segment_ids_are_rejected_before_sending_async() -> None:
+    resend.api_key = "re_test"
+    previous = resend.default_async_http_client
+    client = create_autospec(AsyncHTTPClient, instance=True)
+    client.request = AsyncMock(
+        return_value=(b"{}", 200, {"Content-Type": "application/json"})
+    )
+    resend.default_async_http_client = cast(AsyncHTTPClient, client)
+    try:
+        with pytest.raises(ValueError, match="cannot be `.` or `..`"):
+            await resend.Domains.remove_async("../api-keys/key_id")
+        client.request.assert_not_called()
+    finally:
+        resend.default_async_http_client = previous
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/emails/..",
+        "/emails/./cancel",
+        "/domains/../api-keys/key_id",
+        "/emails/%2E%2E/cancel",
+        "/emails/%2e.",
+        "/emails/.%2E?limit=1",
+    ],
+)
+def test_has_dot_segment(path: str) -> None:
+    assert has_dot_segment(path)
+
+
+@pytest.mark.parametrize(
+    "path",
+    [
+        "/emails/4ef9a417-02e9-4d39-ad75-9611e0fcc33c",
+        "/emails/...",
+        "/emails/..%2Fapi-keys",
+        "/contacts/john.doe@example.com",
+        "/templates?after=..",
+        "/emails/x#/..",
+    ],
+)
+def test_has_no_dot_segment(path: str) -> None:
+    assert not has_dot_segment(path)