diff --git a/AGENTS.md b/AGENTS.md
index d87ab805..51c30048 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -134,4 +134,5 @@ Versions are derived from git tags via `hatch-vcs` — never edit `pyathena/_ver
 
 ### Google-style Docstrings
 
-Use Google-style docstrings for public methods. See existing code for examples.
+Follow the [docstring rules](docs/contributing.md#write-docstrings), which `just lint` checks with ruff's pydocstyle rules for `pyathena/`.
+Mark overrides with `pyathena.util.override` instead of repeating the base method's docstring.
diff --git a/docs/contributing.md b/docs/contributing.md
index c0fbac14..5fc5a779 100644
--- a/docs/contributing.md
+++ b/docs/contributing.md
@@ -71,6 +71,26 @@ External-fork pull requests must not be run in the project's AWS integration CI.
 Do not submit an untested change expecting a maintainer to approve an AWS CI run to validate it.
 Checks that need no AWS access may still run, but their success does not establish integration coverage.
 
+## Write docstrings
+
+Code under `pyathena/` uses [Google-style docstrings](https://google.github.io/styleguide/pyguide.html#38-comments-and-docstrings).
+`just lint` checks them with ruff's pydocstyle rules.
+
+- Modules, packages, public classes, and public functions and methods have a docstring.
+  Describe arguments, return values, and raised exceptions in `Args:`, `Returns:`, and `Raises:` sections.
+- `__init__` describes the constructor arguments in its `Args:` section.
+- A property getter has a one-line docstring; its setter needs none.
+- Magic methods such as `__enter__` and `__iter__` need no docstring.
+- A method that overrides a base class method is decorated with `override` from `pyathena.util`.
+  It needs a docstring only when its behavior differs from the base method; otherwise the API reference shows the base method's docstring.
+  mypy reports a missing decorator, except on an unannotated property.
+- Overrides of fsspec methods are not decorated, because fsspec has no type information, so they need a docstring.
+- New or changed private functions and methods use the same style.
+  ruff does not require them to have a docstring, but checks the docstrings they have.
+
+`per-file-ignores` in `pyproject.toml` lists the `D` codes that each file still has findings for.
+Remove a file's `D` codes when its docstrings are complete, and keep its other codes.
+
 ## Open a pull request
 
 Open a draft pull request with the repository's template completed.
diff --git a/pyathena/__init__.py b/pyathena/__init__.py
index 1e73d195..ee80666d 100644
--- a/pyathena/__init__.py
+++ b/pyathena/__init__.py
@@ -30,7 +30,7 @@
 
 
 class DBAPITypeObject(frozenset[str]):
-    """Type Objects and Constructors
+    """A DB API type object that compares equal to each of its Athena type names.
 
     https://www.python.org/dev/peps/pep-0249/#type-objects-and-constructors
     """
@@ -89,6 +89,8 @@ def connect(*args, **kwargs) -> Connection[Any]:
     SQL queries.
 
     Args:
+        *args: Positional arguments passed to the Connection constructor, in the
+            order of its parameters (``s3_staging_dir``, ``region_name``, ...).
         s3_staging_dir: S3 location to store query results. Required if not
             using workgroups or if the workgroup doesn't have a result location.
             Pass an empty string to explicitly disable S3 staging and skip
@@ -144,6 +146,8 @@ async def aio_connect(*args, **kwargs) -> AioConnection:
     and API calls, keeping the event loop free.
 
     Args:
+        *args: Forwarded to ``AioConnection.create()``, which accepts keyword
+            arguments only.
         **kwargs: Arguments forwarded to ``AioConnection.create()``.
             See :func:`connect` for the full list of supported arguments.
 
diff --git a/pyathena/aio/cursor.py b/pyathena/aio/cursor.py
index 38ef885f..addfc6a5 100644
--- a/pyathena/aio/cursor.py
+++ b/pyathena/aio/cursor.py
@@ -104,7 +104,7 @@ async def execute(
             parameters: Query parameters (optional).
             work_group: Athena workgroup to use (optional).
             s3_staging_dir: S3 location for query results (optional).
-            cache_size: Query result cache size (optional).
+            cache_size: Number of queries to check for result caching (optional).
             cache_expiration_time: Cache expiration time in seconds (optional).
             result_reuse_enable: Enable result reuse (optional).
             result_reuse_minutes: Result reuse duration in minutes (optional).
diff --git a/pyathena/async_cursor.py b/pyathena/async_cursor.py
index 620df9d6..98e351f8 100644
--- a/pyathena/async_cursor.py
+++ b/pyathena/async_cursor.py
@@ -190,7 +190,7 @@ def execute(
             parameters: Query parameters (optional).
             work_group: Athena workgroup to use (optional).
             s3_staging_dir: S3 location for query results (optional).
-            cache_size: Query result cache size in MB (optional).
+            cache_size: Number of queries to check for result caching (optional).
             cache_expiration_time: Cache expiration time in seconds (optional).
             result_reuse_enable: Enable result reuse for identical queries (optional).
             result_reuse_minutes: Result reuse duration in minutes (optional).
diff --git a/pyathena/common.py b/pyathena/common.py
index 963ec459..28a3e0a5 100644
--- a/pyathena/common.py
+++ b/pyathena/common.py
@@ -1232,10 +1232,20 @@ def _cancel(self, query_id: str) -> None:
             raise OperationalError(*e.args) from e
 
     def setinputsizes(self, sizes):  # noqa: B027
-        """Does nothing by default"""
+        """Accept input sizes as DB API 2.0 requires, and ignore them.
+
+        Args:
+            sizes: Sequence of parameter types or sizes.
+        """
 
     def setoutputsize(self, size, column=None):  # noqa: B027
-        """Does nothing by default"""
+        """Accept a column buffer size as DB API 2.0 requires, and ignore it.
+
+        Args:
+            size: Buffer size for large columns.
+            column: Index of the column the size applies to, or None for all
+                large columns.
+        """
 
     def __enter__(self):
         return self
diff --git a/pyathena/cursor.py b/pyathena/cursor.py
index 2e789520..8b91413f 100644
--- a/pyathena/cursor.py
+++ b/pyathena/cursor.py
@@ -107,6 +107,13 @@ def execute(
         Args:
             operation: SQL query string to execute.
             parameters: Query parameters (optional).
+            work_group: Athena workgroup to use for this query.
+            s3_staging_dir: S3 location for query results.
+            cache_size: Number of queries to check for result caching.
+            cache_expiration_time: Cache expiration time in seconds.
+            result_reuse_enable: Enable Athena result reuse for this query.
+            result_reuse_minutes: Minutes to reuse cached results.
+            paramstyle: Parameter style ('qmark' or 'pyformat').
             on_start_query_execution: Callback function called immediately after
                 start_query_execution API is called.
                 Function signature: (query_id: str) -> None
diff --git a/pyathena/filesystem/s3.py b/pyathena/filesystem/s3.py
index abbe270f..4d29fa14 100644
--- a/pyathena/filesystem/s3.py
+++ b/pyathena/filesystem/s3.py
@@ -1964,6 +1964,11 @@ def _call(self, method: str | Callable[..., Any], **kwargs) -> dict[str, Any]:
 
 
 class S3File(AbstractBufferedFile):
+    """A buffered file object for reading and writing an S3 object.
+
+    Instances are returned by ``S3FileSystem.open()``.
+    """
+
     fs: S3FileSystem
 
     def __init__(
diff --git a/pyathena/result_set.py b/pyathena/result_set.py
index dade34f4..45393710 100644
--- a/pyathena/result_set.py
+++ b/pyathena/result_set.py
@@ -753,6 +753,8 @@ def __exit__(self, exc_type, exc_val, exc_tb):
 
 
 class AthenaDictResultSet(AthenaResultSet):
+    """A result set that returns each row as a dictionary keyed by column name."""
+
     # You can override this to use OrderedDict or other dict-like types.
     dict_type: type[Any] = dict
 
diff --git a/pyathena/sqlalchemy/requirements.py b/pyathena/sqlalchemy/requirements.py
index 048e9229..a4d9595b 100644
--- a/pyathena/sqlalchemy/requirements.py
+++ b/pyathena/sqlalchemy/requirements.py
@@ -15,6 +15,8 @@
 
 
 class Requirements(SuiteRequirements):
+    """Features of the Athena dialect for the SQLAlchemy test suite."""
+
     @property
     @override
     def comment_reflection(self):
diff --git a/pyproject.toml b/pyproject.toml
index 414ff78f..40a3530b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -159,22 +159,122 @@ select = [
     "PGH",  # pygrep-hooks
     "G",  # flake8-logging-format
     "PT",  # flake8-pytest-style
+    "D",  # pydocstyle
 ]
 ignore = [
     "RUF059",  # unused-unpacked-variable (too noisy for interface-heavy code)
     "G004",  # logging-f-string (f-strings are preferred for log messages)
+    "D105",  # undocumented-magic-method (protocol methods need no docstring)
 ]
 
+[tool.ruff.lint.pydocstyle]
+convention = "google"
+# Overrides marked with @override inherit the base method's documentation.
+ignore-decorators = ["pyathena.util.override"]
+
 [tool.ruff.lint.per-file-ignores]
 "tests/**" = [
     "RUF012",  # mutable-class-default (test classes often use mutable defaults)
 ]
+"!pyathena/**" = [
+    "D",  # docstring rules apply to the package only
+]
 "pyathena/sqlalchemy/compiler.py" = [
     "N802",  # SQLAlchemy TypeCompiler requires visit_UPPERCASE method names
+    # Missing docstrings (#882)
+    "D100",
+    "D102",
+    "D107",
 ]
 "pyathena/aio/sqlalchemy/base.py" = [
     "N801",  # SQLAlchemy async adapter naming convention (AsyncAdapt_*)
+    # Missing docstrings (#882)
+    "D100",
+    "D102",
+    "D107",
 ]
+# Missing docstrings (#882). Remove a file's D codes once it is documented.
+"pyathena/__init__.py" = ["D104"]
+"pyathena/aio/__init__.py" = ["D104"]
+"pyathena/aio/arrow/__init__.py" = ["D104"]
+"pyathena/aio/arrow/cursor.py" = ["D100", "D107"]
+"pyathena/aio/common.py" = ["D100"]
+"pyathena/aio/connection.py" = ["D100", "D107"]
+"pyathena/aio/cursor.py" = ["D100", "D107"]
+"pyathena/aio/pandas/__init__.py" = ["D104"]
+"pyathena/aio/pandas/cursor.py" = ["D100", "D107"]
+"pyathena/aio/polars/__init__.py" = ["D104"]
+"pyathena/aio/polars/cursor.py" = ["D100", "D107"]
+"pyathena/aio/result_set.py" = ["D100", "D107"]
+"pyathena/aio/s3fs/__init__.py" = ["D104"]
+"pyathena/aio/s3fs/cursor.py" = ["D100", "D107"]
+"pyathena/aio/spark/__init__.py" = ["D104"]
+"pyathena/aio/spark/cursor.py" = ["D100"]
+"pyathena/aio/sqlalchemy/__init__.py" = ["D104"]
+"pyathena/aio/sqlalchemy/arrow.py" = ["D100"]
+"pyathena/aio/sqlalchemy/pandas.py" = ["D100"]
+"pyathena/aio/sqlalchemy/polars.py" = ["D100"]
+"pyathena/aio/sqlalchemy/rest.py" = ["D100"]
+"pyathena/aio/sqlalchemy/s3fs.py" = ["D100"]
+"pyathena/aio/util.py" = ["D100"]
+"pyathena/arrow/__init__.py" = ["D104"]
+"pyathena/arrow/async_cursor.py" = ["D100"]
+"pyathena/arrow/converter.py" = ["D100", "D107"]
+"pyathena/arrow/cursor.py" = ["D100"]
+"pyathena/arrow/result_set.py" = ["D100", "D102", "D107"]
+"pyathena/async_cursor.py" = ["D100", "D102", "D107"]
+"pyathena/common.py" = ["D100", "D102", "D107"]
+"pyathena/connection.py" = ["D100"]
+"pyathena/converter.py" = ["D100", "D102", "D107"]
+"pyathena/cursor.py" = ["D100", "D107"]
+"pyathena/error.py" = ["D100"]
+"pyathena/filesystem/__init__.py" = ["D104"]
+"pyathena/filesystem/s3.py" = ["D100", "D102", "D107"]
+"pyathena/filesystem/s3_async.py" = ["D100", "D102", "D107"]
+"pyathena/filesystem/s3_errors.py" = ["D107"]
+"pyathena/filesystem/s3_executor.py" = ["D100", "D107"]
+"pyathena/filesystem/s3_object.py" = ["D100", "D102", "D107"]
+"pyathena/formatter.py" = ["D100", "D102", "D107"]
+"pyathena/glue.py" = ["D107"]
+"pyathena/model.py" = ["D100", "D102", "D107"]
+"pyathena/options.py" = ["D100"]
+"pyathena/pandas/__init__.py" = ["D104"]
+"pyathena/pandas/async_cursor.py" = ["D100", "D107"]
+"pyathena/pandas/converter.py" = ["D100", "D107"]
+"pyathena/pandas/cursor.py" = ["D100"]
+"pyathena/pandas/reader.py" = ["D100", "D107"]
+"pyathena/pandas/result_set.py" = ["D100", "D102"]
+"pyathena/pandas/util.py" = ["D100"]
+"pyathena/parser.py" = ["D100", "D107"]
+"pyathena/polars/__init__.py" = ["D104"]
+"pyathena/polars/async_cursor.py" = ["D100"]
+"pyathena/polars/converter.py" = ["D100", "D107"]
+"pyathena/polars/cursor.py" = ["D100"]
+"pyathena/polars/result_set.py" = ["D100"]
+"pyathena/result_set.py" = ["D100", "D102", "D107"]
+"pyathena/s3fs/__init__.py" = ["D104"]
+"pyathena/s3fs/async_cursor.py" = ["D100"]
+"pyathena/s3fs/converter.py" = ["D100", "D107"]
+"pyathena/s3fs/cursor.py" = ["D100"]
+"pyathena/s3fs/reader.py" = ["D100"]
+"pyathena/s3fs/result_set.py" = ["D100", "D107"]
+"pyathena/spark/__init__.py" = ["D104"]
+"pyathena/spark/async_cursor.py" = ["D100", "D102"]
+"pyathena/spark/common.py" = ["D100", "D102", "D107"]
+"pyathena/spark/cursor.py" = ["D100", "D102"]
+"pyathena/sqlalchemy/__init__.py" = ["D104"]
+"pyathena/sqlalchemy/array.py" = ["D107"]
+"pyathena/sqlalchemy/arrow.py" = ["D100"]
+"pyathena/sqlalchemy/base.py" = ["D100", "D107"]
+"pyathena/sqlalchemy/map.py" = ["D107"]
+"pyathena/sqlalchemy/pandas.py" = ["D100"]
+"pyathena/sqlalchemy/polars.py" = ["D100"]
+"pyathena/sqlalchemy/preparer.py" = ["D100", "D107"]
+"pyathena/sqlalchemy/requirements.py" = ["D100"]
+"pyathena/sqlalchemy/rest.py" = ["D100"]
+"pyathena/sqlalchemy/s3fs.py" = ["D100"]
+"pyathena/sqlalchemy/struct.py" = ["D107"]
+"pyathena/util.py" = ["D100", "D107"]
 
 [tool.mypy]
 follow_imports = "silent"