diff --git a/swh/model/collections.py b/swh/model/collections.py
--- a/swh/model/collections.py
+++ b/swh/model/collections.py
@@ -3,6 +3,8 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
+"""Utility data structures."""
+
 from collections.abc import Mapping
 from typing import Dict, Generic, Iterable, Optional, Tuple, TypeVar, Union
 
@@ -11,6 +13,11 @@
 
 
 class ImmutableDict(Mapping, Generic[KT, VT]):
+    """A frozen dictionary.
+
+    This class behaves like a dictionary, but internally stores objects in a tuple,
+    so it is both immutable and hashable."""
+
     data: Tuple[Tuple[KT, VT], ...]
 
     def __init__(
diff --git a/swh/model/from_disk.py b/swh/model/from_disk.py
--- a/swh/model/from_disk.py
+++ b/swh/model/from_disk.py
@@ -3,6 +3,13 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
+"""Conversion from filesystem tree to SWH objects.
+
+This module allows reading a tree of directories and files from a local
+filesystem, and convert them to in-memory data structures, which can then
+be exported to SWH data model objects, as defined in :mod:`swh.model.model`.
+"""
+
 import datetime
 import enum
 import fnmatch
diff --git a/swh/model/git_objects.py b/swh/model/git_objects.py
--- a/swh/model/git_objects.py
+++ b/swh/model/git_objects.py
@@ -3,6 +3,30 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
+"""
+Converts SWH model objects to git(-like) objects
+
+Most of the functions in this module take as argument an object from
+:mod:`swh.model.model`, and format it like a git object.
+
+They are the inverse functions of those in :mod:`swh.loader.git.converters`,
+but with extensions, as SWH's model is a superset of Git's:
+
+* extensions of existing types (eg. revision/commit and release/tag dates
+  can be expressed with precision up to milliseconds, to support formatting
+  Mercurial objects)
+* new types, for SWH's specific needs (:class:`swh.model.model.RawExtrinsicMetadata`
+  and :class:`swh.model.model.ExtID`)
+* support for somewhat corrupted git objects that we need to reproduce
+
+This is used for two purposes:
+
+* Format manifests that can be hashed to produce :ref:`intrinsic identifiers
+  <persistent-identifiers>`
+* Write git objects to reproduce git repositories that were ingested in the archive.
+"""
+
+
 from __future__ import annotations
 
 import datetime
diff --git a/swh/model/model.py b/swh/model/model.py
--- a/swh/model/model.py
+++ b/swh/model/model.py
@@ -3,6 +3,18 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
+"""
+Implementation of Software Heritage's data model
+
+See :ref:`data-model` for an overview of the data model.
+
+The classes defined in this module are immutable
+`attrs objects <https://attrs.org/>`__ and enums.
+
+All classes define a ``from_dict`` class method and a ``to_dict``
+method to convert between them and msgpack-serializable objects.
+"""
+
 from abc import ABCMeta, abstractmethod
 import datetime
 from enum import Enum
diff --git a/swh/model/swhids.py b/swh/model/swhids.py
--- a/swh/model/swhids.py
+++ b/swh/model/swhids.py
@@ -3,6 +3,15 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
+"""
+Classes to represent :ref:`SWH persistend IDentifiers <persistent-identifiers>`.
+
+:class:`CoreSWHID` represents a SWHID with no qualifier, and :class:`QualifiedSWHID`
+represents a SWHID that may have qualifiers.
+:class:`ExtendedSWHID` extends the definition of SWHID to other object types,
+and is used internally in Software Heritage; it does not support qualifiers.
+"""
+
 from __future__ import annotations
 
 import enum