diff --git a/.gitignore b/.gitignore
index 95f08686e..88c381afc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -80,3 +80,5 @@ _version.py
 
 .core_typemap_version
 core_typemap.pkl
+
+/venv
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 21e9e8ae7..1bdde5b62 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## PyNWB 3.0.0 (Upcoming)
 
 ### Enhancements and minor changes
+- Added `__all__` to modules. @bendichter [#2021](https://github.com/NeurodataWithoutBorders/pynwb/pull/2021)
 - Added `pynwb.read_nwb` convenience method to simplify reading an NWBFile written with any backend @h-mayorquin [#1994](https://github.com/NeurodataWithoutBorders/pynwb/pull/1994)
 - Added support for NWB schema 2.8.0. @rly [#2001](https://github.com/NeurodataWithoutBorders/pynwb/pull/2001)
   - Removed `SpatialSeries.bounds` field that was not functional. This will be fixed in a future release. @rly [#1907](https://github.com/NeurodataWithoutBorders/pynwb/pull/1907), [#1996](https://github.com/NeurodataWithoutBorders/pynwb/pull/1996)
diff --git a/src/pynwb/__init__.py b/src/pynwb/__init__.py
index 7931322a8..5d16c7d5f 100644
--- a/src/pynwb/__init__.py
+++ b/src/pynwb/__init__.py
@@ -613,6 +613,32 @@ def read_nwb(**kwargs):
 from hdmf.data_utils import DataChunkIterator  # noqa: F401,E402
 from hdmf.backends.hdf5 import H5DataIO  # noqa: F401,E402
 
+__all__ = [
+    # Functions
+    'get_type_map',
+    'get_manager',
+    'load_namespaces', 
+    'available_namespaces',
+    'register_class',
+    'register_map',
+    'get_class',
+    'load_type_config',
+    'get_loaded_type_config',
+    'unload_type_config',
+    'read_nwb',
+    'get_nwbfile_version',
+    
+    # Classes
+    'NWBHDF5IO',
+    'NWBContainer',
+    'NWBData', 
+    'TimeSeries',
+    'ProcessingModule',
+    'NWBFile',
+    'DataChunkIterator',
+    'H5DataIO'
+]
+
 
 
 from ._due import due, BibTeX  # noqa: E402
diff --git a/src/pynwb/base.py b/src/pynwb/base.py
index 8b4daf48f..6e2d4c5b7 100644
--- a/src/pynwb/base.py
+++ b/src/pynwb/base.py
@@ -12,6 +12,17 @@
 from .core import NWBDataInterface, MultiContainerInterface, NWBData
 
 
+__all__ = [
+    'ProcessingModule',
+    'TimeSeries',
+    'Image',
+    'ImageReferences',
+    'Images',
+    'TimeSeriesReferenceVectorData',
+    'TimeSeriesReference'
+]
+
+
 @register_class('ProcessingModule', CORE_NAMESPACE)
 class ProcessingModule(MultiContainerInterface):
     """ Processing module. This is a container for one or more containers
diff --git a/src/pynwb/behavior.py b/src/pynwb/behavior.py
index d4d43d515..2aa9472ea 100644
--- a/src/pynwb/behavior.py
+++ b/src/pynwb/behavior.py
@@ -7,6 +7,17 @@
 from .misc import IntervalSeries
 from .base import TimeSeries
 
+__all__ = [
+    'SpatialSeries',
+    'BehavioralEpochs',
+    'BehavioralEvents',
+    'BehavioralTimeSeries',
+    'PupilTracking',
+    'EyeTracking',
+    'CompassDirection',
+    'Position'
+]
+
 
 @register_class('SpatialSeries', CORE_NAMESPACE)
 class SpatialSeries(TimeSeries):
diff --git a/src/pynwb/core.py b/src/pynwb/core.py
index f9ae2bd2f..7a656adcc 100644
--- a/src/pynwb/core.py
+++ b/src/pynwb/core.py
@@ -13,6 +13,17 @@
 from pynwb import get_type_map
 
 
+__all__ = [
+    'NWBMixin',
+    'NWBContainer',
+    'NWBDataInterface',
+    'NWBData',
+    'ScratchData',
+    'NWBTable',
+    'MultiContainerInterface'
+]
+
+
 def _not_parent(arg):
     return arg['name'] != 'parent'
 
diff --git a/src/pynwb/device.py b/src/pynwb/device.py
index f842776ae..31e490f0a 100644
--- a/src/pynwb/device.py
+++ b/src/pynwb/device.py
@@ -3,6 +3,7 @@
 from . import register_class, CORE_NAMESPACE
 from .core import NWBContainer
 
+__all__ = ['Device']
 
 @register_class('Device', CORE_NAMESPACE)
 class Device(NWBContainer):
diff --git a/src/pynwb/ecephys.py b/src/pynwb/ecephys.py
index 07d584a4f..739264e21 100644
--- a/src/pynwb/ecephys.py
+++ b/src/pynwb/ecephys.py
@@ -11,6 +11,16 @@
 from .core import NWBContainer, NWBDataInterface, MultiContainerInterface
 from .device import Device
 
+__all__ = [
+    'ElectrodeGroup',
+    'ElectricalSeries',
+    'SpikeEventSeries',
+    'EventDetection',
+    'LFP',
+    'FilteredEphys',
+    'FeatureExtraction'
+]
+
 
 @register_class('ElectrodeGroup', CORE_NAMESPACE)
 class ElectrodeGroup(NWBContainer):
diff --git a/src/pynwb/epoch.py b/src/pynwb/epoch.py
index 9cccc5db5..931080788 100644
--- a/src/pynwb/epoch.py
+++ b/src/pynwb/epoch.py
@@ -7,6 +7,7 @@
 from . import register_class, CORE_NAMESPACE
 from .base import TimeSeries, TimeSeriesReferenceVectorData, TimeSeriesReference
 
+__all__ = ['TimeIntervals']
 
 @register_class('TimeIntervals', CORE_NAMESPACE)
 class TimeIntervals(DynamicTable):
diff --git a/src/pynwb/file.py b/src/pynwb/file.py
index a447c126d..84dc1b5b8 100644
--- a/src/pynwb/file.py
+++ b/src/pynwb/file.py
@@ -26,6 +26,16 @@
 from .core import NWBContainer, NWBDataInterface, MultiContainerInterface, ScratchData, LabelledDict
 
 
+__all__ = [
+    'LabMetaData',
+    'Subject',
+    'NWBFile',
+    'ElectrodeTable',
+    'TrialTable',
+    'InvalidTimesTable'
+]
+
+
 def _not_parent(arg):
     return arg['name'] != 'parent'
 
diff --git a/src/pynwb/icephys.py b/src/pynwb/icephys.py
index ec44a2bd8..4e32094ee 100644
--- a/src/pynwb/icephys.py
+++ b/src/pynwb/icephys.py
@@ -11,6 +11,24 @@
 from .core import NWBContainer
 from .device import Device
 
+__all__ = [
+    'IntracellularElectrode',
+    'PatchClampSeries',
+    'CurrentClampSeries',
+    'IZeroClampSeries',
+    'CurrentClampStimulusSeries',
+    'VoltageClampSeries',
+    'VoltageClampStimulusSeries',
+    'IntracellularElectrodesTable',
+    'IntracellularStimuliTable',
+    'IntracellularResponsesTable',
+    'IntracellularRecordingsTable',
+    'SimultaneousRecordingsTable',
+    'SequentialRecordingsTable',
+    'RepetitionsTable',
+    'ExperimentalConditionsTable'
+]
+
 
 def ensure_unit(self, name, current_unit, unit, nwb_version):
     """A helper to ensure correct unit used.
diff --git a/src/pynwb/image.py b/src/pynwb/image.py
index c775297d7..519d24004 100644
--- a/src/pynwb/image.py
+++ b/src/pynwb/image.py
@@ -17,6 +17,16 @@
 from .device import Device
 
 
+__all__ = [
+    'ImageSeries',
+    'IndexSeries',
+    'OpticalSeries',
+    'GrayscaleImage',
+    'RGBImage',
+    'RGBAImage'
+]
+
+
 @register_class('ImageSeries', CORE_NAMESPACE)
 class ImageSeries(TimeSeries):
     '''
diff --git a/src/pynwb/misc.py b/src/pynwb/misc.py
index 14c2e08d1..8f7383d59 100644
--- a/src/pynwb/misc.py
+++ b/src/pynwb/misc.py
@@ -11,6 +11,13 @@
 from .ecephys import ElectrodeGroup
 from hdmf.common import DynamicTable, DynamicTableRegion
 
+__all__ = [
+    'AnnotationSeries',
+    'AbstractFeatureSeries',
+    'IntervalSeries',
+    'Units',
+    'DecompositionSeries'
+]
 
 @register_class('AnnotationSeries', CORE_NAMESPACE)
 class AnnotationSeries(TimeSeries):
diff --git a/src/pynwb/ogen.py b/src/pynwb/ogen.py
index af11842e4..f433d1bc2 100644
--- a/src/pynwb/ogen.py
+++ b/src/pynwb/ogen.py
@@ -5,6 +5,10 @@
 from .core import NWBContainer
 from .device import Device
 
+__all__ = [
+    'OptogeneticStimulusSite',
+    'OptogeneticSeries'
+]
 
 @register_class('OptogeneticStimulusSite', CORE_NAMESPACE)
 class OptogeneticStimulusSite(NWBContainer):
diff --git a/src/pynwb/ophys.py b/src/pynwb/ophys.py
index 6f1483079..660af4cb9 100644
--- a/src/pynwb/ophys.py
+++ b/src/pynwb/ophys.py
@@ -11,6 +11,20 @@
 from .core import NWBContainer, MultiContainerInterface, NWBDataInterface
 from .device import Device
 
+__all__ = [
+    'OpticalChannel',
+    'ImagingPlane',
+    'OnePhotonSeries',
+    'TwoPhotonSeries',
+    'CorrectedImageStack',
+    'MotionCorrection',
+    'PlaneSegmentation',
+    'ImageSegmentation',
+    'RoiResponseSeries',
+    'DfOverF',
+    'Fluorescence'
+]
+
 
 @register_class('OpticalChannel', CORE_NAMESPACE)
 class OpticalChannel(NWBContainer):
diff --git a/src/pynwb/resources.py b/src/pynwb/resources.py
index acdc22b12..e2d0acda4 100644
--- a/src/pynwb/resources.py
+++ b/src/pynwb/resources.py
@@ -2,6 +2,7 @@
 from . import get_type_map as tm
 from hdmf.utils import docval, get_docval
 
+__all__ = ['HERD']
 
 class HERD(hdmf_HERD):
     """
diff --git a/src/pynwb/spec.py b/src/pynwb/spec.py
index fe97b6eae..7c3a65173 100644
--- a/src/pynwb/spec.py
+++ b/src/pynwb/spec.py
@@ -8,6 +8,19 @@
 from . import CORE_NAMESPACE
 
 
+__all__ = [
+    'NWBRefSpec',
+    'NWBAttributeSpec',
+    'NWBLinkSpec',
+    'NWBDtypeSpec',
+    'NWBDatasetSpec',
+    'NWBGroupSpec',
+    'NWBNamespace',
+    'NWBNamespaceBuilder',
+    'export_spec'  # Re-exported from hdmf.spec.write
+]
+
+
 def __swap_inc_def(cls):
     args = get_docval(cls.__init__)
     clsname = 'NWB%s' % cls.__name__
diff --git a/src/pynwb/testing/icephys_testutils.py b/src/pynwb/testing/icephys_testutils.py
index 3de4619d4..aed8c2653 100644
--- a/src/pynwb/testing/icephys_testutils.py
+++ b/src/pynwb/testing/icephys_testutils.py
@@ -60,10 +60,10 @@ def create_icephys_testfile(filename=None, add_custom_columns=True, randomize_da
     :param randomize_data: Randomize data values in the stimulus and response
     :type randomize_data: bool
 
-    :returns: NWBFile object with icephys data created for writing. NOTE: If filename is provided then
-              the file is written to disk, but the function does not read the file back. If
-              you want to use the file from disk then you will need to read it with NWBHDF5IO.
-    :rtype: NWBFile
+    :returns: :py:class:`~pynwb.file.NWBFile` object with icephys data created for writing. NOTE: If filename is
+              provided then the file is written to disk, but the function does not read the file back. If
+              you want to use the file from disk then you will need to read it with :py:class:`~pynwb.NWBHDF5IO`.
+    :rtype: :py:class:`~pynwb.file.NWBFile`
     """
     nwbfile = NWBFile(
             session_description='my first synthetic recording',
diff --git a/src/pynwb/validate.py b/src/pynwb/validate.py
index 880f860a6..ddd93f2e5 100644
--- a/src/pynwb/validate.py
+++ b/src/pynwb/validate.py
@@ -14,6 +14,12 @@
 from pynwb.spec import NWBDatasetSpec, NWBGroupSpec, NWBNamespace
 
 
+__all__ = [
+    'validate',
+    'get_cached_namespaces_to_validate'
+]
+
+
 def _print_errors(validation_errors: list):
     if validation_errors:
         print(" - found the following errors:", file=sys.stderr)