diff --git a/README.md b/README.md
index 5420357..4c78146 100644
--- a/README.md
+++ b/README.md
@@ -53,7 +53,7 @@ The function `is_bdew_working_day` considers both national **and** state wide ho
 ```python
 from datetime import date
 
-from bdew_datetimes.periods import is_bdew_working_day
+from bdew_datetimes import is_bdew_working_day
 
 assert is_bdew_working_day(date(2023, 1, 1)) is False  # Neujahr (national holiday)
 assert is_bdew_working_day(date(2023, 1, 2)) is True  # regular weekday
@@ -66,7 +66,7 @@ You can also get the next or previous working day for any date:
 ```python
 from datetime import date
 
-from bdew_datetimes.periods import get_next_working_day, get_previous_working_day
+from bdew_datetimes import get_next_working_day, get_previous_working_day
 
 assert get_next_working_day(date(2023, 1, 1)) == date(2023, 1, 2)  # the next working day after Neujahr
 assert get_previous_working_day(date(2023, 1, 1)) == date(2022, 12, 30)  # the last working day of 2022
@@ -75,10 +75,13 @@ assert get_next_working_day(date(2023, 1, 20)) == date(2023, 1, 23)  # the next
 
 ### Calculate Statutory Periods
 Statutory periods define the maximum time between e.g. the EDIFACT message for the "Anmeldung" and the actual start of supply ("Lieferbeginn").
+
 ```python
 from datetime import date
 
-from bdew_datetimes.periods import DayType, EndDateType, Period, add_frist
+from bdew_datetimes import add_frist
+from bdew_datetimes import Period
+from bdew_datetimes.enums import DayType, EndDateType
 
 # Eingang der Anmeldung des LFN erfolgt am 04.07.2016. Der Mindestzeitraum von zehn WT
 # beginnt am 05.07.2016 und endet am 18.07.2016. Frühestes zulässiges Anmeldedatum
@@ -86,20 +89,22 @@ from bdew_datetimes.periods import DayType, EndDateType, Period, add_frist
 # des vorgenannten Tages zugeordnet wird.
 eingang_der_anmeldung = date(2016, 7, 4)
 gesetzliche_frist = Period(
-    10,
-    DayType.WORKING_DAY,
-    end_date_type=EndDateType.EXCLUSIVE
-    # lieferbeginn is the exclusive end of the previous supply contract
+  10,
+  DayType.WORKING_DAY,
+  end_date_type=EndDateType.EXCLUSIVE
+  # lieferbeginn is the exclusive end of the previous supply contract
 )
 fruehest_moeglicher_lieferbeginn = add_frist(eingang_der_anmeldung, gesetzliche_frist)
 assert fruehest_moeglicher_lieferbeginn == date(2016, 7, 19)
 ```
 ### Calculate "Liefer- and Fristenmonate"
 Liefer- and Fristenmonat are concepts used in MaBiS and GPKE:
+
 ```python
 from datetime import date
 
-from bdew_datetimes.periods import get_nth_working_day_of_month, MonthType
+from bdew_datetimes import get_nth_working_day_of_month
+from bdew_datetimes.enums import MonthType
 
 # returns the 18th working day of the current month in Germany
 get_nth_working_day_of_month(18)
diff --git a/src/bdew_datetimes/__init__.py b/src/bdew_datetimes/__init__.py
index 516b4dc..62eeeb2 100644
--- a/src/bdew_datetimes/__init__.py
+++ b/src/bdew_datetimes/__init__.py
@@ -2,9 +2,25 @@
 bdew_datetimes is a package that models the BDEW holiday, which is relevant for German utilities
 """
 
-from pytz import timezone
+from .calendar import BdewDefinedHolidays, create_bdew_calendar
+from .german_time_zone import GERMAN_TIME_ZONE
+from .models import Period
+from .periods import (
+    add_frist,
+    get_next_working_day,
+    get_nth_working_day_of_month,
+    get_previous_working_day,
+    is_bdew_working_day,
+)
 
-from .calendar import create_bdew_calendar
-
-GERMAN_TIME_ZONE = timezone("Europe/Berlin")
-__all__ = ["GERMAN_TIME_ZONE", "create_bdew_calendar"]
+__all__ = [
+    "create_bdew_calendar",
+    "BdewDefinedHolidays",
+    "Period",
+    "is_bdew_working_day",
+    "get_next_working_day",
+    "get_previous_working_day",
+    "add_frist",
+    "get_nth_working_day_of_month",
+    "GERMAN_TIME_ZONE",
+]
diff --git a/src/bdew_datetimes/calendar.py b/src/bdew_datetimes/calendar.py
index e4b5fcb..471d451 100644
--- a/src/bdew_datetimes/calendar.py
+++ b/src/bdew_datetimes/calendar.py
@@ -78,3 +78,6 @@ def create_bdew_calendar() -> HolidaySum:
         # https://github.com/vacanza/python-holidays/blob/v0.53/holidays/holiday_base.py#L1164
         result.language = original_language_before_adding_subdivisions
     return result
+
+
+__all__ = ["BdewDefinedHolidays", "create_bdew_calendar"]
diff --git a/src/bdew_datetimes/enums.py b/src/bdew_datetimes/enums.py
new file mode 100644
index 0000000..485ada4
--- /dev/null
+++ b/src/bdew_datetimes/enums.py
@@ -0,0 +1,69 @@
+"""enums used inside the package"""
+
+from enum import Enum
+
+
+class Division(Enum):
+    """
+    Allows to distinguish divisions used by German utilities, German "Sparte".
+    """
+
+    STROM = 1  #: electricity
+    GAS = 2  #: gas
+
+
+class DayType(str, Enum):
+    """
+    An enum to differentiate between calendar days and working days.
+    """
+
+    WORKING_DAY = "WT"  #: working day, German "Werktag"
+    CALENDAR_DAY = "KT"  #: calendar day, German "Kalendertag"
+
+
+class EndDateType(Enum):
+    """
+    An enum to distinguish inclusive and exclusive end dates.
+    """
+
+    INCLUSIVE = 1
+    """
+    If a contract ends with the year 2022 and the end date is denoted as "2022-12-31",
+    then the end date is inclusive. Most dates in human (spoken) communication are meant
+    inclusively.
+    """
+
+    EXCLUSIVE = 2
+    """
+    If a contract ends with the year 2022 and the end date is denoted as "2023-01-01",
+    then the end date is exclusive. Most end dates handled by technical systems are meant
+    exclusively.
+    """
+
+
+class MonthType(Enum):
+    """
+    When calculating periods defined as 'nth working day of a month' the
+    BNetzA regulations distinguish between two types of month which are
+    modelled in this enum.
+    Some periods refer to the "Liefermonat", others to the "Fristenmonat".
+    """
+
+    LIEFERMONAT = 1
+    """
+    The "Liefermonat" is the month in which the supply starts.
+    """
+    FRISTENMONAT = 2
+    """
+    The grid operators prefer a key date based handling of supply contracts.
+    The key date in these cases is usually expressed as a specific working day
+    in the so called "Fristenmonat".
+    The "Fristenmonat" starts at the first day of the month
+    _before_ the "Liefermonat".
+    Quote: 'Nach der Festlegung BK6-06-009 (GPKE) der Monat vor dem Liefermonat.'
+    """
+    # pylint:disable=line-too-long
+    # source: https://www.bundesnetzagentur.de/DE/Beschlusskammern/1_GZ/BK6-GZ/_bis_2010/2006/BK6-06-009/BK6-06-009_Beschluss_download.pdf?__blob=publicationFile&v=5
+
+
+__all__ = ["Division", "EndDateType", "MonthType", "DayType"]
diff --git a/src/bdew_datetimes/german_strom_and_gas_tag.py b/src/bdew_datetimes/german_strom_and_gas_tag.py
index ea406e0..6ffa79a 100644
--- a/src/bdew_datetimes/german_strom_and_gas_tag.py
+++ b/src/bdew_datetimes/german_strom_and_gas_tag.py
@@ -4,7 +4,6 @@
 """
 
 from datetime import datetime, time
-from enum import Enum
 from typing import Callable
 
 # The problem with the stdlib zoneinfo is, that the availability of timezones
@@ -14,16 +13,9 @@
 # datasource for timezone information.
 from pytz import utc
 
-from bdew_datetimes import GERMAN_TIME_ZONE
+from bdew_datetimes.enums import Division
 
-
-class Division(Enum):
-    """
-    Allows to distinguish divisions used by German utilities, German "Sparte".
-    """
-
-    STROM = 1  #: electricity
-    GAS = 2  #: gas
+from .german_time_zone import GERMAN_TIME_ZONE
 
 
 def _get_german_local_time(date_time: datetime) -> time:
@@ -102,3 +94,6 @@ def is_xtag_limit(date_time: datetime, division: Division) -> bool:
             f"The division must either be 'Strom' or 'Gas': '{division}'"
         )
     return xtag_evaluator(date_time)
+
+
+__all__ = ["is_gastag_limit", "is_stromtag_limit"]
diff --git a/src/bdew_datetimes/german_time_zone.py b/src/bdew_datetimes/german_time_zone.py
new file mode 100644
index 0000000..16bbde8
--- /dev/null
+++ b/src/bdew_datetimes/german_time_zone.py
@@ -0,0 +1,6 @@
+"""static timezone object for Berlin/Germany"""
+
+from pytz import timezone
+
+GERMAN_TIME_ZONE = timezone("Europe/Berlin")
+__all__ = ["GERMAN_TIME_ZONE"]
diff --git a/src/bdew_datetimes/models.py b/src/bdew_datetimes/models.py
new file mode 100644
index 0000000..6e9d89c
--- /dev/null
+++ b/src/bdew_datetimes/models.py
@@ -0,0 +1,57 @@
+"""model classes used in this package"""
+
+from dataclasses import dataclass
+from typing import Literal, Union
+
+from bdew_datetimes.enums import DayType, EndDateType
+
+_DayTyp = Union[DayType, Literal["WT", "KT"]]
+
+
+@dataclass
+class Period:
+    """
+    A period is a German "Frist": A tuple that consists of a number of days and a day type.
+    """
+
+    number_of_days: int
+    """
+    number of days (might be any value <0, >0 or ==0)
+    """
+    day_type: DayType
+    """
+    the kind of days to add/subtract
+    """
+
+    def __init__(
+        self,
+        number_of_days: int,
+        day_type: _DayTyp,
+        end_date_type: EndDateType = EndDateType.EXCLUSIVE,
+    ):
+        """
+        Initialize the Period by providing a number of days and a day_type which define the period.
+
+        """
+        self.number_of_days = number_of_days
+        # If the Period is about something ending (e.g. a contract), then the user may
+        # provide an end_date_type.
+        # Internally we handle all end dates as exclusive, because:
+        # https://hf-kklein.github.io/exclusive_end_dates.github.io/
+        if end_date_type == EndDateType.INCLUSIVE:
+            if self.number_of_days > 0:
+                self.number_of_days = self.number_of_days - 1
+            elif self.number_of_days < 0:
+                self.number_of_days = self.number_of_days + 1
+        if isinstance(day_type, DayType):
+            pass
+        elif isinstance(day_type, str):
+            day_type = DayType(day_type)
+        else:
+            raise ValueError(
+                f"'{day_type}' is not an allowed value; Check the typing"
+            )
+        self.day_type: DayType = day_type
+
+
+__all__ = ["Period"]
diff --git a/src/bdew_datetimes/periods.py b/src/bdew_datetimes/periods.py
index 94013b8..dd64e11 100644
--- a/src/bdew_datetimes/periods.py
+++ b/src/bdew_datetimes/periods.py
@@ -5,15 +5,16 @@
 """
 
 import datetime
-from dataclasses import dataclass
 from datetime import date
-from enum import Enum
-from typing import Literal, Optional, Union
+from typing import Optional
 
 from dateutil.relativedelta import relativedelta
 from holidays import SAT, SUN  # type:ignore[attr-defined]
 
-from bdew_datetimes import GERMAN_TIME_ZONE, create_bdew_calendar
+from bdew_datetimes.calendar import create_bdew_calendar
+from bdew_datetimes.enums import DayType, EndDateType, MonthType
+from bdew_datetimes.german_time_zone import GERMAN_TIME_ZONE
+from bdew_datetimes.models import Period
 
 # https://www.bundesnetzagentur.de/DE/Beschlusskammern/1_GZ/BK6-GZ/2020/BK6-20-160/Mitteilung_Nr_2/Leseversion_GPKE.pdf
 # pages 15 onwards
@@ -24,84 +25,6 @@
 """
 
 
-class DayType(str, Enum):
-    """
-    An enum to differentiate between calendar days and working days.
-    """
-
-    WORKING_DAY = "WT"  #: working day, German "Werktag"
-    CALENDAR_DAY = "KT"  #: calendar day, German "Kalendertag"
-
-
-class EndDateType(Enum):
-    """
-    An enum to distinguish inclusive and exclusive end dates.
-    """
-
-    INCLUSIVE = 1
-    """
-    If a contract ends with the year 2022 and the end date is denoted as "2022-12-31",
-    then the end date is inclusive. Most dates in human (spoken) communication are meant
-    inclusively.
-    """
-
-    EXCLUSIVE = 2
-    """
-    If a contract ends with the year 2022 and the end date is denoted as "2023-01-01",
-    then the end date is exclusive. Most end dates handled by technical systems are meant
-    exclusively.
-    """
-
-
-_DayTyp = Union[DayType, Literal["WT", "KT"]]
-
-
-@dataclass
-class Period:
-    """
-    A period is a German "Frist": A tuple that consists of a number of days and a day type.
-    """
-
-    number_of_days: int
-    """
-    number of days (might be any value <0, >0 or ==0)
-    """
-    day_type: DayType
-    """
-    the kind of days to add/subtract
-    """
-
-    def __init__(
-        self,
-        number_of_days: int,
-        day_type: _DayTyp,
-        end_date_type: EndDateType = EndDateType.EXCLUSIVE,
-    ):
-        """
-        Initialize the Period by providing a number of days and a day_type which define the period.
-
-        """
-        self.number_of_days = number_of_days
-        # If the Period is about something ending (e.g. a contract), then the user may
-        # provide an end_date_type.
-        # Internally we handle all end dates as exclusive, because:
-        # https://hf-kklein.github.io/exclusive_end_dates.github.io/
-        if end_date_type == EndDateType.INCLUSIVE:
-            if self.number_of_days > 0:
-                self.number_of_days = self.number_of_days - 1
-            elif self.number_of_days < 0:
-                self.number_of_days = self.number_of_days + 1
-        if isinstance(day_type, DayType):
-            pass
-        elif isinstance(day_type, str):
-            day_type = DayType(day_type)
-        else:
-            raise ValueError(
-                f"'{day_type}' is not an allowed value; Check the typing"
-            )
-        self.day_type: DayType = day_type
-
-
 def is_bdew_working_day(candidate: date) -> bool:
     """
     Returns true if and only if the given candidate is a day relevant for the period calculation.
@@ -172,31 +95,6 @@ def add_frist(start: date, period: Period) -> date:
     return result
 
 
-class MonthType(Enum):
-    """
-    When calculating periods defined as 'nth working day of a month' the
-    BNetzA regulations distinguish between two types of month which are
-    modelled in this enum.
-    Some periods refer to the "Liefermonat", others to the "Fristenmonat".
-    """
-
-    LIEFERMONAT = 1
-    """
-    The "Liefermonat" is the month in which the supply starts.
-    """
-    FRISTENMONAT = 2
-    """
-    The grid operators prefer a key date based handling of supply contracts.
-    The key date in these cases is usually expressed as a specific working day
-    in the so called "Fristenmonat".
-    The "Fristenmonat" starts at the first day of the month
-    _before_ the "Liefermonat".
-    Quote: 'Nach der Festlegung BK6-06-009 (GPKE) der Monat vor dem Liefermonat.'
-    """
-    # pylint:disable=line-too-long
-    # source: https://www.bundesnetzagentur.de/DE/Beschlusskammern/1_GZ/BK6-GZ/_bis_2010/2006/BK6-06-009/BK6-06-009_Beschluss_download.pdf?__blob=publicationFile&v=5
-
-
 def get_nth_working_day_of_month(
     number_of_working_day_in_month: int,
     month_type: MonthType = MonthType.LIEFERMONAT,
@@ -233,3 +131,13 @@ def get_nth_working_day_of_month(
     else:
         raise ValueError(f"Unhandled month_type {month_type}")
     return result
+
+
+# pylint:disable=duplicate-code
+__all__ = [
+    "is_bdew_working_day",
+    "get_next_working_day",
+    "get_previous_working_day",
+    "add_frist",
+    "get_nth_working_day_of_month",
+]
diff --git a/tests/test_german_strom_and_gas_tag.py b/tests/test_german_strom_and_gas_tag.py
index 375297c..e51d829 100644
--- a/tests/test_german_strom_and_gas_tag.py
+++ b/tests/test_german_strom_and_gas_tag.py
@@ -2,14 +2,14 @@
 
 import pytest
 
-from bdew_datetimes import GERMAN_TIME_ZONE
+from bdew_datetimes.enums import Division
 from bdew_datetimes.german_strom_and_gas_tag import (
-    Division,
     has_no_utc_offset,
     is_gastag_limit,
     is_stromtag_limit,
     is_xtag_limit,
 )
+from bdew_datetimes.german_time_zone import GERMAN_TIME_ZONE
 
 
 @pytest.mark.parametrize(
diff --git a/tests/test_period.py b/tests/test_period.py
index bae512a..b359184 100644
--- a/tests/test_period.py
+++ b/tests/test_period.py
@@ -2,12 +2,9 @@
 
 import pytest
 
+from bdew_datetimes.enums import DayType, EndDateType, MonthType
+from bdew_datetimes.models import Period, _DayTyp
 from bdew_datetimes.periods import (
-    DayType,
-    EndDateType,
-    MonthType,
-    Period,
-    _DayTyp,
     add_frist,
     get_next_working_day,
     get_nth_working_day_of_month,