diff --git a/CHANGES.rst b/CHANGES.rst
index ffae49ad..3b2abc20 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -6,7 +6,7 @@ Changelog
 
 Minor changes:
 
-- ...
+- add ``__all__`` variable to each modules in ``icalendar`` package
 
 Breaking changes:
 
diff --git a/src/icalendar/cal.py b/src/icalendar/cal.py
index 3c250596..83553f2a 100644
--- a/src/icalendar/cal.py
+++ b/src/icalendar/cal.py
@@ -764,3 +764,7 @@ def example(cls, name) -> Calendar:
 # These are read only singleton, so one instance is enough for the module
 types_factory = TypesFactory()
 component_factory = ComponentFactory()
+
+__all__ = ["Alarm", "Calendar", "Component", "ComponentFactory", "Event",
+           "FreeBusy", "INLINE", "Journal", "Timezone", "TimezoneDaylight",
+           "TimezoneStandard", "Todo", "component_factory", "get_example"]
diff --git a/src/icalendar/caselessdict.py b/src/icalendar/caselessdict.py
index 097dcd99..03bec28e 100644
--- a/src/icalendar/caselessdict.py
+++ b/src/icalendar/caselessdict.py
@@ -106,3 +106,6 @@ def sorted_items(self):
         Items not specified in canonical_order will appear at the end.
         """
         return canonsort_items(self, self.canonical_order)
+
+
+__all__ = ["canonsort_keys", "canonsort_items", "CaselessDict"]
diff --git a/src/icalendar/cli.py b/src/icalendar/cli.py
index ac53963c..e9d0eb72 100755
--- a/src/icalendar/cli.py
+++ b/src/icalendar/cli.py
@@ -83,5 +83,8 @@ def main():
             for event in calendar.walk('vevent'):
                 argv.output.write(view(event) + '\n\n')
 
+
+__all__ = ["main", "view"]
+
 if __name__ == '__main__':
     main()
diff --git a/src/icalendar/parser.py b/src/icalendar/parser.py
index 10d95ad6..47ca858b 100644
--- a/src/icalendar/parser.py
+++ b/src/icalendar/parser.py
@@ -384,3 +384,11 @@ def from_ical(cls, st):
 
 # XXX: what kind of hack is this? import depends to be at end
 from icalendar.prop import vText
+
+
+__all__ = ["Contentline", "Contentlines", "FOLD", "NAME", "NEWLINE",
+           "Parameters", "QUNSAFE_CHAR", "QUOTABLE", "UNSAFE_CHAR", "dquote",
+           "escape_char", "escape_string", "foldline", "param_value", "q_join",
+           "q_split", "tzid_from_dt", "uFOLD", "unescape_char",
+           "unescape_list_or_string", "unescape_string", "validate_param_value",
+           "validate_token"]
diff --git a/src/icalendar/parser_tools.py b/src/icalendar/parser_tools.py
index 47ad8092..ee9d02ca 100644
--- a/src/icalendar/parser_tools.py
+++ b/src/icalendar/parser_tools.py
@@ -48,3 +48,7 @@ def data_encode(data: Union[ICAL_TYPE, dict, list], encoding=DEFAULT_ENCODING) -
         return list(map(data_encode, data))
     else:
         return data
+
+
+__all__ = ["DEFAULT_ENCODING", "SEQUENCE_TYPES", "ICAL_TYPE" "data_encode", "from_unicode",
+           "to_unicode"]
diff --git a/src/icalendar/prop.py b/src/icalendar/prop.py
index 0a4c1b0e..509179ec 100644
--- a/src/icalendar/prop.py
+++ b/src/icalendar/prop.py
@@ -1122,3 +1122,11 @@ def from_ical(self, name, value):
         type_class = self.for_property(name)
         decoded = type_class.from_ical(value)
         return decoded
+
+
+__all__ = ["DURATION_REGEX", "TimeBase", "TypesFactory", "WEEKDAY_RULE",
+           "tzid_from_dt", "vBinary", "vBoolean", "vCalAddress",
+           "vCategory", "vDDDLists", "vDDDTypes", "vDate", "vDatetime",
+           "vDuration", "vFloat", "vFrequency", "vGeo", "vInline", "vInt",
+           "vMonth", "vPeriod", "vRecur", "vSkip", "vText", "vTime",
+           "vUTCOffset", "vUri", "vWeekday"]
diff --git a/src/icalendar/tests/test_equality.py b/src/icalendar/tests/test_equality.py
index 8dadb109..5cb1cac8 100644
--- a/src/icalendar/tests/test_equality.py
+++ b/src/icalendar/tests/test_equality.py
@@ -5,7 +5,7 @@
 except ImportError:
     pytz = None
 from icalendar.prop import *
-from datetime import datetime, date, timedelta
+from datetime import datetime, date, time, timedelta
 import pytest
 
 def assert_equal(actual_value, expected_value):
diff --git a/src/icalendar/timezone/provider.py b/src/icalendar/timezone/provider.py
index 18697b9a..8330c395 100644
--- a/src/icalendar/timezone/provider.py
+++ b/src/icalendar/timezone/provider.py
@@ -43,3 +43,5 @@ def uses_pytz(self) -> bool:
     @abstractmethod
     def uses_zoneinfo(self) -> bool:
         """Whether we use zoneinfo."""
+
+__all__ = ["TZProvider"]
diff --git a/src/icalendar/tools.py b/src/icalendar/tools.py
index b9af20b7..896aa7a6 100644
--- a/src/icalendar/tools.py
+++ b/src/icalendar/tools.py
@@ -31,3 +31,5 @@ def uid(host_name='example.com', unique=''):
         unique = unique or UIDGenerator.rnd_string()
         today = to_unicode(vDatetime(datetime.today()).to_ical())
         return vText(f'{today}-{unique}@{host_name}')
+
+__all__ = ["UIDGenerator"]