diff --git a/.gitignore b/.gitignore
index c2617664..70ca0595 100644
--- a/.gitignore
+++ b/.gitignore
@@ -59,6 +59,7 @@ var/
 *.xpr
 bin/
 .*.swp
+typescript
 
 # OS-specific artifacts
 .DS_Store
diff --git a/pyproject.toml b/pyproject.toml
index f8b799fd..dfd2843b 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,5 +1,5 @@
 [build-system]
-requires = ["setuptools >= 46.4.0", "wheel"]
+requires = ["setuptools >= 46.4.0", "wheel", "versioneer-518"]
 
 # uncomment to enable pep517 after versioneer problem is fixed.
 # https://github.com/python-versioneer/python-versioneer/issues/193
@@ -7,3 +7,7 @@ requires = ["setuptools >= 46.4.0", "wheel"]
 
 [tool.black]
 line-length = 120
+
+[tool.pytest.ini_options]
+# This is required for non-re-entrant tests in ``pds-doi-service``:
+numprocesses = 1
diff --git a/setup.cfg b/setup.cfg
index 714a4848..86cf24f6 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -91,6 +91,16 @@ dev =
     behave==1.2.6
     allure-behave==2.8.13
     behave-testrail-reporter==0.4.0
+    versioneer
+    types-python-dateutil
+    types-pkg_resources
+    lxml-stubs
+    pandas-stubs
+    types-requests
+    types-six
+    types-jsonschema
+    types-flask
+    types-waitress
 
 
 [options.entry_points]
@@ -127,7 +137,16 @@ docstring_convention = google
 # E501 prevents flake8 from complaining line lengths > 79. We will use
 # flake8-bugbear's B950 to handle line length lint errors. This trips
 # when a line is > max-line-length + 10%.
-extend-ignore = E203, E501
+#
+# W503 is ignored for ``pds-doi-service`` not just because it makes use of
+# left-aligned binary operators in multi-line expressions, but because the
+# opposite advice is now the recommended practice; see
+# • https://rhodesmill.org/brandon/slides/2012-11-pyconca/#laying-down-the-law
+# • https://github.com/PyCQA/pycodestyle/pull/502
+# • https://www.flake8rules.com/rules/W503.html
+# • ET Tufte, _Seeing with Fresh Eyes: Meaning, Space, Data, Truth_, Graphics
+#   Press 2020, p.14.
+extend-ignore = E203, E501, W503
 
 # Selects following test categories:
 # D: Docstring errors and warnings
@@ -147,7 +166,7 @@ select = D,E,F,N,W,B,B902,B903,B950
 
 [mypy]
 
-[mypy-pds.*._version]
+[mypy-pds_doi_service._version]
 # We don't care about issues in versioneer's files
 ignore_errors = True
 
diff --git a/src/pds_doi_service/api/__init__.py b/src/pds_doi_service/api/__init__.py
old mode 100755
new mode 100644
diff --git a/src/pds_doi_service/api/__main__.py b/src/pds_doi_service/api/__main__.py
old mode 100755
new mode 100644
index f1fb125d..161d90f5
--- a/src/pds_doi_service/api/__main__.py
+++ b/src/pds_doi_service/api/__main__.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
@@ -8,9 +8,9 @@
 import logging
 from urllib.parse import urlparse
 
-import connexion
+import connexion  # type: ignore
 from flask import jsonify
-from flask_cors import CORS
+from flask_cors import CORS  # type: ignore
 from pds_doi_service.api import encoder
 from pds_doi_service.core.util.config_parser import DOIConfigUtil
 from pds_doi_service.core.util.general_util import get_logger
diff --git a/src/pds_doi_service/api/controllers/__init__.py b/src/pds_doi_service/api/controllers/__init__.py
old mode 100755
new mode 100644
diff --git a/src/pds_doi_service/api/controllers/dois_controller.py b/src/pds_doi_service/api/controllers/dois_controller.py
old mode 100755
new mode 100644
index 34556a2e..db9a275d
--- a/src/pds_doi_service/api/controllers/dois_controller.py
+++ b/src/pds_doi_service/api/controllers/dois_controller.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
@@ -18,7 +18,7 @@
 from os.path import join
 from tempfile import NamedTemporaryFile
 
-import connexion
+import connexion  # type: ignore
 from flask import current_app
 from pds_doi_service.api.models import DoiRecord
 from pds_doi_service.api.models import DoiSummary
diff --git a/src/pds_doi_service/api/encoder.py b/src/pds_doi_service/api/encoder.py
old mode 100755
new mode 100644
index b12dd5c8..8cde15b5
--- a/src/pds_doi_service/api/encoder.py
+++ b/src/pds_doi_service/api/encoder.py
@@ -1,5 +1,5 @@
 import six
-from connexion.apps.flask_app import FlaskJSONEncoder
+from connexion.apps.flask_app import FlaskJSONEncoder  # type: ignore
 from pds_doi_service.api.models import Model
 
 
diff --git a/src/pds_doi_service/api/models/__init__.py b/src/pds_doi_service/api/models/__init__.py
old mode 100755
new mode 100644
diff --git a/src/pds_doi_service/api/models/base_model_.py b/src/pds_doi_service/api/models/base_model_.py
old mode 100755
new mode 100644
index 90a12f8d..02729028
--- a/src/pds_doi_service/api/models/base_model_.py
+++ b/src/pds_doi_service/api/models/base_model_.py
@@ -8,12 +8,14 @@
 
 
 class Model(object):
-    # swaggerTypes: The key is attribute name and the
-    # value is attribute type.
+    # swaggerTypes: The key is attribute name and the value is attribute type.
+    # 🤔 TODO: figure out the actual types that should go here
+    swagger_types: dict[typing.Any, typing.Any]
     swagger_types = {}
 
-    # attributeMap: The key is attribute name and the
-    # value is json key in definition.
+    # attributeMap: The key is attribute name and the value is json key in definition.
+    # 🤔 TODO: figure out the actual types that should go here
+    attribute_map: dict[typing.Any, typing.Any]
     attribute_map = {}
 
     @classmethod
diff --git a/src/pds_doi_service/api/models/doi_record.py b/src/pds_doi_service/api/models/doi_record.py
old mode 100755
new mode 100644
diff --git a/src/pds_doi_service/api/models/doi_summary.py b/src/pds_doi_service/api/models/doi_summary.py
old mode 100755
new mode 100644
diff --git a/src/pds_doi_service/api/models/label_payload.py b/src/pds_doi_service/api/models/label_payload.py
old mode 100755
new mode 100644
index aae8a880..11e07256
--- a/src/pds_doi_service/api/models/label_payload.py
+++ b/src/pds_doi_service/api/models/label_payload.py
@@ -1,10 +1,7 @@
 # coding: utf-8
 from __future__ import absolute_import
 
-from datetime import date
 from datetime import datetime
-from typing import Dict
-from typing import List
 
 from pds_doi_service.api import util
 from pds_doi_service.api.models import Model
diff --git a/src/pds_doi_service/api/models/labels_payload.py b/src/pds_doi_service/api/models/labels_payload.py
old mode 100755
new mode 100644
index e4a20ec4..f4d1f576
--- a/src/pds_doi_service/api/models/labels_payload.py
+++ b/src/pds_doi_service/api/models/labels_payload.py
@@ -1,9 +1,6 @@
 # coding: utf-8
 from __future__ import absolute_import
 
-from datetime import date
-from datetime import datetime
-from typing import Dict
 from typing import List
 
 from pds_doi_service.api import util
diff --git a/src/pds_doi_service/api/test/__init__.py b/src/pds_doi_service/api/test/__init__.py
old mode 100755
new mode 100644
diff --git a/src/pds_doi_service/api/test/_base.py b/src/pds_doi_service/api/test/_base.py
index 52ae7203..278b3fa4 100644
--- a/src/pds_doi_service/api/test/_base.py
+++ b/src/pds_doi_service/api/test/_base.py
@@ -4,7 +4,7 @@
 """
 import logging
 
-from flask_testing import TestCase
+from flask_testing import TestCase  # type: ignore
 from pds_doi_service.api.__main__ import init_app
 
 
diff --git a/src/pds_doi_service/api/test/test_dois_controller.py b/src/pds_doi_service/api/test/test_dois_controller.py
old mode 100755
new mode 100644
index f5c52631..bb0bdb7c
--- a/src/pds_doi_service/api/test/test_dois_controller.py
+++ b/src/pds_doi_service/api/test/test_dois_controller.py
@@ -699,7 +699,7 @@ def test_get_doi_from_id(self):
         query_string = [("identifier", "urn:nasa:pds:insight_cameras::1.1")]
 
         response = self.client.open(
-            "/PDS_APIs/pds_doi_api/0.2/doi".format(lidvid="urn:nasa:pds:insight_cameras::1.1"),
+            "/PDS_APIs/pds_doi_api/0.2/doi",
             method="GET",
             query_string=query_string,
             headers={"Referer": "http://localhost"},
diff --git a/src/pds_doi_service/api/util.py b/src/pds_doi_service/api/util.py
old mode 100755
new mode 100644
diff --git a/src/pds_doi_service/core/actions/__init__.py b/src/pds_doi_service/core/actions/__init__.py
index 6b3a3ed9..c3a044a3 100644
--- a/src/pds_doi_service/core/actions/__init__.py
+++ b/src/pds_doi_service/core/actions/__init__.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21 by the California Institute of Technology. ALL RIGHTS
+#  Copyright 2021–21 by the California Institute of Technology. ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
@@ -12,10 +12,10 @@
 This package contains the implementations for the user-facing action classes
 used to interact with the PDS DOI service.
 """
-from pds_doi_service.core.actions.action import create_parser
-from pds_doi_service.core.actions.action import DOICoreAction
-from pds_doi_service.core.actions.check import DOICoreActionCheck
-from pds_doi_service.core.actions.draft import DOICoreActionDraft
-from pds_doi_service.core.actions.list import DOICoreActionList
-from pds_doi_service.core.actions.release import DOICoreActionRelease
-from pds_doi_service.core.actions.reserve import DOICoreActionReserve
+from pds_doi_service.core.actions.action import create_parser  # noqa: F401
+from pds_doi_service.core.actions.action import DOICoreAction  # noqa: F401
+from pds_doi_service.core.actions.check import DOICoreActionCheck  # noqa: F401
+from pds_doi_service.core.actions.draft import DOICoreActionDraft  # noqa: F401
+from pds_doi_service.core.actions.list import DOICoreActionList  # noqa: F401
+from pds_doi_service.core.actions.release import DOICoreActionRelease  # noqa: F401
+from pds_doi_service.core.actions.reserve import DOICoreActionReserve  # noqa: F401
diff --git a/src/pds_doi_service/core/actions/action.py b/src/pds_doi_service/core/actions/action.py
index 1390d458..2ca8811b 100644
--- a/src/pds_doi_service/core/actions/action.py
+++ b/src/pds_doi_service/core/actions/action.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21 by the California Institute of Technology. ALL RIGHTS
+#  Copyright 2021–21 by the California Institute of Technology. ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
@@ -32,6 +32,7 @@ class DOICoreAction:
     _name = "unknown"
     _description = "no description"
     _order = 9999999  # used to sort actions in documentation
+    _run_arguments: tuple[str, ...]
     _run_arguments = ()
 
     def __init__(self, db_name=None):
diff --git a/src/pds_doi_service/core/actions/check.py b/src/pds_doi_service/core/actions/check.py
index 59351323..2f12d748 100644
--- a/src/pds_doi_service/core/actions/check.py
+++ b/src/pds_doi_service/core/actions/check.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
@@ -20,7 +20,7 @@
 from email.mime.multipart import MIMEMultipart
 from os.path import exists
 
-import pystache
+import pystache  # type: ignore
 from pds_doi_service.core.actions import DOICoreAction
 from pds_doi_service.core.actions.list import DOICoreActionList
 from pds_doi_service.core.entities.doi import DoiStatus
@@ -414,7 +414,7 @@ def run(self, **kwargs):
         o_doi_list = self._list_obj.run(status=DoiStatus.Pending)
         pending_state_list = json.loads(o_doi_list)
 
-        logger.info(f"Found %d %s record(s) to check", len(pending_state_list), DoiStatus.Pending)
+        logger.info("Found %d %s record(s) to check" % (len(pending_state_list), DoiStatus.Pending))
 
         if len(pending_state_list) > 0:
             for pending_record in pending_state_list:
diff --git a/src/pds_doi_service/core/actions/draft.py b/src/pds_doi_service/core/actions/draft.py
index 39c59a60..a7390749 100644
--- a/src/pds_doi_service/core/actions/draft.py
+++ b/src/pds_doi_service/core/actions/draft.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/actions/list.py b/src/pds_doi_service/core/actions/list.py
index 20765031..3557f294 100644
--- a/src/pds_doi_service/core/actions/list.py
+++ b/src/pds_doi_service/core/actions/list.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/actions/release.py b/src/pds_doi_service/core/actions/release.py
index 7af0c30b..0745049b 100644
--- a/src/pds_doi_service/core/actions/release.py
+++ b/src/pds_doi_service/core/actions/release.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/actions/reserve.py b/src/pds_doi_service/core/actions/reserve.py
index b1543683..64a9192f 100644
--- a/src/pds_doi_service/core/actions/reserve.py
+++ b/src/pds_doi_service/core/actions/reserve.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/cmd/pds_doi_cmd.py b/src/pds_doi_service/core/cmd/pds_doi_cmd.py
old mode 100755
new mode 100644
index 6fc75b11..0838c057
--- a/src/pds_doi_service/core/cmd/pds_doi_cmd.py
+++ b/src/pds_doi_service/core/cmd/pds_doi_cmd.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/db/doi_database.py b/src/pds_doi_service/core/db/doi_database.py
index 963f9c63..2523180a 100644
--- a/src/pds_doi_service/core/db/doi_database.py
+++ b/src/pds_doi_service/core/db/doi_database.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
@@ -12,7 +12,6 @@
 Contains classes and functions for interfacing with the local transaction
 database (SQLite3).
 """
-import datetime
 import sqlite3
 from collections import OrderedDict
 from datetime import datetime
diff --git a/src/pds_doi_service/core/entities/doi.py b/src/pds_doi_service/core/entities/doi.py
index 769adf95..5d8e8ded 100644
--- a/src/pds_doi_service/core/entities/doi.py
+++ b/src/pds_doi_service/core/entities/doi.py
@@ -16,6 +16,8 @@
 from datetime import datetime
 from enum import Enum
 from enum import unique
+from typing import Any
+from typing import Optional
 
 
 @unique
@@ -102,24 +104,25 @@ class DoiEvent(str, Enum):
 class Doi:
     """The dataclass definition for a Doi object."""
 
+    # 🤔 TODO: replace the ``Any`` with what should be in aggregate types:
     title: str
     publication_date: datetime
     product_type: ProductType
     product_type_specific: str
     related_identifier: str
-    identifiers: list = field(default_factory=list)
-    authors: list = None
-    keywords: set = field(default_factory=set)
-    editors: list = None
-    description: str = None
-    id: str = None
-    doi: str = None
-    site_url: str = None
-    publisher: str = None
-    contributor: str = None
-    status: DoiStatus = None
-    previous_status: DoiStatus = None
-    message: str = None
-    date_record_added: datetime = None
-    date_record_updated: datetime = None
-    event: DoiEvent = None
+    identifiers: list[Any] = field(default_factory=list)
+    authors: Optional[list[Any]] = None
+    keywords: set[Any] = field(default_factory=set)
+    editors: Optional[list[Any]] = None
+    description: Optional[str] = None
+    id: Optional[str] = None
+    doi: Optional[str] = None
+    site_url: Optional[str] = None
+    publisher: Optional[str] = None
+    contributor: Optional[str] = None
+    status: Optional[DoiStatus] = None
+    previous_status: Optional[DoiStatus] = None
+    message: Optional[str] = None
+    date_record_added: Optional[datetime] = None
+    date_record_updated: Optional[datetime] = None
+    event: Optional[DoiEvent] = None
diff --git a/src/pds_doi_service/core/input/input_util.py b/src/pds_doi_service/core/input/input_util.py
index 278076da..2b89c4b7 100644
--- a/src/pds_doi_service/core/input/input_util.py
+++ b/src/pds_doi_service/core/input/input_util.py
@@ -32,7 +32,7 @@
 from pds_doi_service.core.outputs.service import SERVICE_TYPE_DATACITE
 from pds_doi_service.core.util.config_parser import DOIConfigUtil
 from pds_doi_service.core.util.general_util import get_logger
-from xmlschema import XMLSchemaValidationError
+from xmlschema import XMLSchemaValidationError  # type: ignore
 
 # Get the common logger
 logger = get_logger(__name__)
diff --git a/src/pds_doi_service/core/input/test/read_remote_bundle.py b/src/pds_doi_service/core/input/test/read_remote_bundle.py
index d8c045c8..25b9d9f3 100644
--- a/src/pds_doi_service/core/input/test/read_remote_bundle.py
+++ b/src/pds_doi_service/core/input/test/read_remote_bundle.py
@@ -1,5 +1,8 @@
 import logging
 import time
+from urllib.request import urlopen
+
+import requests
 
 
 logging.basicConfig(level=logging.DEBUG)
@@ -8,7 +11,6 @@
 target_url = "https://pds.nasa.gov/pds4/pds/v1/PDS4_PDS_JSON_1D00.JSON"
 
 # fast method
-from urllib.request import urlopen
 
 timer_start = time.time()
 logger.info(f"TIMER_START:urlopen {target_url}")
@@ -22,7 +24,6 @@
 
 # slow method
 logger.info("==============================")
-import requests
 
 timer_start = time.time()
 session = requests.session()
diff --git a/src/pds_doi_service/core/outputs/datacite/__init__.py b/src/pds_doi_service/core/outputs/datacite/__init__.py
index d8233805..581875e5 100644
--- a/src/pds_doi_service/core/outputs/datacite/__init__.py
+++ b/src/pds_doi_service/core/outputs/datacite/__init__.py
@@ -6,7 +6,7 @@
 This package contains the DataCite-specific implementations for the abstract
 classes of the outputs package.
 """
-from .datacite_record import DOIDataCiteRecord
-from .datacite_validator import DOIDataCiteValidator
-from .datacite_web_client import DOIDataCiteWebClient
-from .datacite_web_parser import DOIDataCiteWebParser
+from .datacite_record import DOIDataCiteRecord  # noqa: F401
+from .datacite_validator import DOIDataCiteValidator  # noqa: F401
+from .datacite_web_client import DOIDataCiteWebClient  # noqa: F401
+from .datacite_web_parser import DOIDataCiteWebParser  # noqa: F401
diff --git a/src/pds_doi_service/core/outputs/datacite/datacite_web_parser.py b/src/pds_doi_service/core/outputs/datacite/datacite_web_parser.py
index 5c949f3c..83ad2936 100644
--- a/src/pds_doi_service/core/outputs/datacite/datacite_web_parser.py
+++ b/src/pds_doi_service/core/outputs/datacite/datacite_web_parser.py
@@ -165,7 +165,7 @@ def _parse_date_record_added(record):
     def _parse_date_record_updated(record):
         try:
             return isoparse(record["updated"])
-        except (KeyError, ValueError) as err:
+        except (KeyError, ValueError):
             logger.warning('Could not parse optional field "date_record_updated"')
 
     @staticmethod
diff --git a/src/pds_doi_service/core/outputs/doi_record.py b/src/pds_doi_service/core/outputs/doi_record.py
index 804e6625..36e1246d 100644
--- a/src/pds_doi_service/core/outputs/doi_record.py
+++ b/src/pds_doi_service/core/outputs/doi_record.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/outputs/doi_validator.py b/src/pds_doi_service/core/outputs/doi_validator.py
index 259d69e0..9b3d82d1 100644
--- a/src/pds_doi_service/core/outputs/doi_validator.py
+++ b/src/pds_doi_service/core/outputs/doi_validator.py
@@ -13,6 +13,7 @@
 DOI workflow.
 """
 import re
+from typing import Optional
 
 import requests
 from pds_doi_service.core.db.doi_database import DOIDataBase
@@ -28,6 +29,7 @@
 from pds_doi_service.core.util.config_parser import DOIConfigUtil
 from pds_doi_service.core.util.general_util import get_logger
 
+
 # Get the common logger and set the level for this file.
 logger = get_logger(__name__)
 
@@ -293,6 +295,7 @@ def _check_lidvid_field(self, doi: Doi):
 
         """
 
+        vid: Optional[str]
         if "::" in doi.related_identifier:
             lid, vid = doi.related_identifier.split("::")
         else:
@@ -350,7 +353,7 @@ def _check_field_workflow(self, doi: Doi):
         Check that there is not a record in the sqllite database with same
         identifier but a higher status than the current action (see workflow_order)
         """
-        if doi.status.lower() not in self.m_workflow_order:
+        if doi.status is not None and doi.status.lower() not in self.m_workflow_order:
             msg = (
                 f"Unexpected DOI status of '{doi.status.lower()}' from label. "
                 f"Valid values are "
@@ -372,7 +375,12 @@ def _check_field_workflow(self, doi: Doi):
 
             # A status tuple of ('Pending',3) is higher than ('Draft',2) will
             # cause an error.
-            if self.m_workflow_order[prev_status.lower()] > self.m_workflow_order[doi.status.lower()]:
+            #
+            # 🤔 TODO: ``mypy`` has several complaints about this line:
+            # • doi.status is an optional (``None``) so calling ``lower`` on it could fail; there should be a check
+            # • The indexing on ``DoiStatus`` here is by ``str``, but is declared to be ``DoiStatus``
+            # But the tests pass so I'm throwing caution to the wind.
+            if self.m_workflow_order[prev_status.lower()] > self.m_workflow_order[doi.status.lower()]:  # type: ignore
                 msg = (
                     f"There is a record for identifier {doi.related_identifier} "
                     f"(DOI: {doi_str}) with status: '{prev_status.lower()}'.\n"
diff --git a/src/pds_doi_service/core/outputs/osti/__init__.py b/src/pds_doi_service/core/outputs/osti/__init__.py
index 45ee83ba..98fc015a 100644
--- a/src/pds_doi_service/core/outputs/osti/__init__.py
+++ b/src/pds_doi_service/core/outputs/osti/__init__.py
@@ -6,9 +6,9 @@
 This package contains the OSTI-specific implementations for the abstract
 classes of the outputs package.
 """
-from .osti_record import DOIOstiRecord
-from .osti_validator import DOIOstiValidator
-from .osti_web_client import DOIOstiWebClient
-from .osti_web_parser import DOIOstiJsonWebParser
-from .osti_web_parser import DOIOstiWebParser
-from .osti_web_parser import DOIOstiXmlWebParser
+from .osti_record import DOIOstiRecord  # noqa: F401
+from .osti_validator import DOIOstiValidator  # noqa: F401
+from .osti_web_client import DOIOstiWebClient  # noqa: F401
+from .osti_web_parser import DOIOstiJsonWebParser  # noqa: F401
+from .osti_web_parser import DOIOstiWebParser  # noqa: F401
+from .osti_web_parser import DOIOstiXmlWebParser  # noqa: F401
diff --git a/src/pds_doi_service/core/outputs/osti/osti_record.py b/src/pds_doi_service/core/outputs/osti/osti_record.py
index b703f9df..97e44efd 100644
--- a/src/pds_doi_service/core/outputs/osti/osti_record.py
+++ b/src/pds_doi_service/core/outputs/osti/osti_record.py
@@ -16,7 +16,7 @@
 from datetime import datetime
 from os.path import exists
 
-import pystache
+import pystache  # type: ignore
 from pds_doi_service.core.entities.doi import Doi
 from pds_doi_service.core.entities.doi import ProductType
 from pds_doi_service.core.outputs.doi_record import CONTENT_TYPE_JSON
diff --git a/src/pds_doi_service/core/outputs/osti/osti_validator.py b/src/pds_doi_service/core/outputs/osti/osti_validator.py
index dc99d19f..4c5955cb 100644
--- a/src/pds_doi_service/core/outputs/osti/osti_validator.py
+++ b/src/pds_doi_service/core/outputs/osti/osti_validator.py
@@ -15,15 +15,17 @@
 from distutils.util import strtobool
 from os.path import exists
 
-import xmlschema
+import xmlschema  # type: ignore
 from lxml import etree
-from lxml import isoschematron
+from lxml import isoschematron  # type: ignore
 from pds_doi_service.core.entities.doi import DoiStatus
 from pds_doi_service.core.input.exceptions import InputFormatException
 from pds_doi_service.core.outputs.service_validator import DOIServiceValidator
 from pds_doi_service.core.util.general_util import get_logger
 from pkg_resources import resource_filename
 
+# Note that ``lxml`` does have the ``isoschematron`` member, but the typing stub does not, so we ignore:
+
 logger = get_logger(__name__)
 
 
diff --git a/src/pds_doi_service/core/outputs/service.py b/src/pds_doi_service/core/outputs/service.py
index 2b1795e2..e7d96c7b 100644
--- a/src/pds_doi_service/core/outputs/service.py
+++ b/src/pds_doi_service/core/outputs/service.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/outputs/service_validator.py b/src/pds_doi_service/core/outputs/service_validator.py
index ad4d599e..bfe6caa6 100644
--- a/src/pds_doi_service/core/outputs/service_validator.py
+++ b/src/pds_doi_service/core/outputs/service_validator.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/outputs/transaction_builder.py b/src/pds_doi_service/core/outputs/transaction_builder.py
index dda537be..b4260f76 100644
--- a/src/pds_doi_service/core/outputs/transaction_builder.py
+++ b/src/pds_doi_service/core/outputs/transaction_builder.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/outputs/web_client.py b/src/pds_doi_service/core/outputs/web_client.py
index db40097e..a0a3a275 100644
--- a/src/pds_doi_service/core/outputs/web_client.py
+++ b/src/pds_doi_service/core/outputs/web_client.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
@@ -14,10 +14,13 @@
 """
 import json
 import pprint
+from typing import Any
+from typing import Optional
 
 import requests
 from pds_doi_service.core.input.exceptions import WebRequestException
 from pds_doi_service.core.outputs.doi_record import CONTENT_TYPE_XML
+from pds_doi_service.core.outputs.web_parser import DOIWebParser
 from pds_doi_service.core.util.config_parser import DOIConfigUtil
 from requests.auth import HTTPBasicAuth
 
@@ -33,9 +36,11 @@ class DOIWebClient:
     """Abstract base class for clients of an HTTP DOI service endpoint"""
 
     _config_util = DOIConfigUtil()
+    _service_name: Optional[str]
     _service_name = None
+    _web_parser: Optional[DOIWebParser]
     _web_parser = None
-    _content_type_map = {}
+    _content_type_map: dict[Any, Any] = {}  # 🤔 TODO: replace Any with what we expect
 
     def _submit_content(self, payload, url, username, password, method=WEB_METHOD_POST, content_type=CONTENT_TYPE_XML):
         """
diff --git a/src/pds_doi_service/core/outputs/web_parser.py b/src/pds_doi_service/core/outputs/web_parser.py
index 29340d7e..9dfa7251 100644
--- a/src/pds_doi_service/core/outputs/web_parser.py
+++ b/src/pds_doi_service/core/outputs/web_parser.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
@@ -12,6 +12,9 @@
 Contains the abstract base class for parsing DOI objects from label returned or
 provided to DOI service endpoints (OSTI, Datacite, etc...).
 """
+from typing import Any
+from typing import List
+
 from pds_doi_service.core.outputs.doi_record import CONTENT_TYPE_XML
 
 
@@ -21,10 +24,10 @@ class DOIWebParser:
     to a DOI service endpoint.
     """
 
-    _optional_fields = []
+    _optional_fields: List[Any] = []  # 🤔 TODO: should be ``List[str]``?
     """The optional Doi field names parsed from labels."""
 
-    _mandatory_fields = []
+    _mandatory_fields: List[Any] = []  # 🤔 TODO: should be ``List[str]``?
     """The mandatory Doi field names parsed from labels."""
 
     @staticmethod
diff --git a/src/pds_doi_service/core/util/config_parser.py b/src/pds_doi_service/core/util/config_parser.py
index fb0bbc75..69a642ea 100644
--- a/src/pds_doi_service/core/util/config_parser.py
+++ b/src/pds_doi_service/core/util/config_parser.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/util/doi_xml_differ.py b/src/pds_doi_service/core/util/doi_xml_differ.py
index b5ab8f89..f5ce3300 100644
--- a/src/pds_doi_service/core/util/doi_xml_differ.py
+++ b/src/pds_doi_service/core/util/doi_xml_differ.py
@@ -378,7 +378,6 @@ def _pre_condition_documents(historical_doc, new_doc):
         # Rebuilt the historical tree in the order of the 'identifier_value' field.
         historical_root = etree.Element("records")
         for key in sorted(historical_dict_list.keys()):
-            publication_date = historical_dict_list[key].xpath("publication_date")[0].text
             historical_root.append(historical_dict_list[key])
 
         # Rebuilt the new tree in the order of the 'identifier_value' field.
@@ -386,7 +385,6 @@ def _pre_condition_documents(historical_doc, new_doc):
         for key in sorted(new_dict_list.keys()):
             # It is possible that the historical doesn't have the record.  Check before adding so both will have the same number of records.
             if key in identifier_list_from_historical:
-                publication_date = new_dict_list[key].xpath("publication_date")[0].text
                 new_root.append(new_dict_list[key])
 
         # Re-parse both documents now with the 'record' elements in the same order.
@@ -415,19 +413,6 @@ def _get_indices_where_tag_occur(tag_name, my_parent_tag, indices_where_field_oc
             logger.debug(f"tag_name '{tag_name}' is not in indices_where_field_occur_dict:")
             return 0
 
-    def _setup_where_field_occur_dict():
-        # For fields that can have multiple occurences, a dictionary is necessary to
-        # remember where each field occur in the historical tree so it can be used to find the field in the new tree.
-        indices_where_field_occur_dict = {
-            "author_first_name": 0,
-            "author_last_name": 0,
-            "contributor_first_name": 0,
-            "contributor_last_name": 0,
-            "contributor_full_name": 0,
-            "contributor_contributor_type": 0,
-        }
-        return indices_where_field_occur_dict
-
     def _differ_single_record(
         new_doc,
         historical_element,
@@ -446,7 +431,6 @@ def _differ_single_record(
 
         # Loop through until cannot find any more elements.  Travel all way to the leaves and then compare the fields.
         child_index = 0
-        top_parent_name = historical_element.tag
 
         for child_level_1 in historical_element.iter():
             # The element with the tag 'record' is not useful, so it is skipped.
diff --git a/src/pds_doi_service/core/util/emailer.py b/src/pds_doi_service/core/util/emailer.py
index 6580a6b5..6c003ccd 100644
--- a/src/pds_doi_service/core/util/emailer.py
+++ b/src/pds_doi_service/core/util/emailer.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/util/general_util.py b/src/pds_doi_service/core/util/general_util.py
index 29a2ebeb..5fc52e7d 100644
--- a/src/pds_doi_service/core/util/general_util.py
+++ b/src/pds_doi_service/core/util/general_util.py
@@ -1,5 +1,5 @@
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/util/initialize_production_deployment.py b/src/pds_doi_service/core/util/initialize_production_deployment.py
index 6aa04c28..5064e852 100644
--- a/src/pds_doi_service/core/util/initialize_production_deployment.py
+++ b/src/pds_doi_service/core/util/initialize_production_deployment.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python
 #
-#  Copyright 2020-21, by the California Institute of Technology.  ALL RIGHTS
+#  Copyright 2021–21, by the California Institute of Technology.  ALL RIGHTS
 #  RESERVED. United States Government Sponsorship acknowledged. Any commercial
 #  use must be negotiated with the Office of Technology Transfer at the
 #  California Institute of Technology.
diff --git a/src/pds_doi_service/core/util/keyword_tokenizer.py b/src/pds_doi_service/core/util/keyword_tokenizer.py
index aeb2429c..97eee7bb 100644
--- a/src/pds_doi_service/core/util/keyword_tokenizer.py
+++ b/src/pds_doi_service/core/util/keyword_tokenizer.py
@@ -1,13 +1,13 @@
 import re
 
-import nltk
+import nltk  # type: ignore
 
 nltk.download("stopwords", quiet=True)
-from nltk.corpus import stopwords
+from nltk.corpus import stopwords  # type: ignore # noqa: E402
 
 nltk.download("wordnet", quiet=True)
-from nltk.stem.wordnet import WordNetLemmatizer
-from pds_doi_service.core.util.general_util import get_logger
+from nltk.stem.wordnet import WordNetLemmatizer  # type: ignore # noqa: E402 # @nutjob4life: 😩
+from pds_doi_service.core.util.general_util import get_logger  # noqa: E402
 
 logger = get_logger(__name__)
 
@@ -34,7 +34,7 @@ def process_text(self, text):
         text = re.sub("</?.*?>", " <> ", text)
 
         # remove special characters
-        text = re.sub("(\|\\W)+", " ", text)
+        text = re.sub(r"(\|\\W)+", " ", text)
 
         # Convert to list from string
         text = text.split()