diff --git a/.github/workflows/python-test.yml b/.github/workflows/python-test.yml
index 2caa6ff..b801c63 100644
--- a/.github/workflows/python-test.yml
+++ b/.github/workflows/python-test.yml
@@ -20,7 +20,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install pytest coverage pytest-cov six mock
+          pip install pytest coverage pytest-cov mock
           if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
           pip install -e .
       - name: Test with pytest
@@ -46,7 +46,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install pytest coverage pytest-cov six mock
+          pip install pytest coverage pytest-cov mock
           if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
           pip install -e .
       - name: Test with pytest
diff --git a/setup.py b/setup.py
index b9e61b5..8fb478f 100755
--- a/setup.py
+++ b/setup.py
@@ -40,10 +40,6 @@
 DESCRIPTION = 'Config file reading, writing and validation.'
 URL = 'https://github.com/DiffSK/configobj'
 
-REQUIRES = """
-    six
-"""
-
 VERSION = ''
 with closing(open(os.path.join(__here__, 'src', PACKAGES[0], '_version.py'), 'r')) as handle:
     for line in handle.readlines():
@@ -120,7 +116,6 @@
     py_modules=MODULES,
     package_dir={'': 'src'},
     packages=PACKAGES,
-    install_requires=[i.strip() for i in REQUIRES.splitlines() if i.strip()],
     python_requires='>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*',
     classifiers=CLASSIFIERS,
     keywords=KEYWORDS,
diff --git a/src/configobj/__init__.py b/src/configobj/__init__.py
index 0580b65..2515d9f 100644
--- a/src/configobj/__init__.py
+++ b/src/configobj/__init__.py
@@ -31,7 +31,6 @@
     # Python 2.7
     from collections import Mapping
 
-import six
 from ._version import __version__
 
 # imported lazily to avoid startup performance hit if it isn't used
@@ -507,11 +506,11 @@ def __getitem__(self, key):
         """Fetch the item and do string interpolation."""
         val = dict.__getitem__(self, key)
         if self.main.interpolation:
-            if isinstance(val, six.string_types):
+            if isinstance(val, (str, )):
                 return self._interpolate(key, val)
             if isinstance(val, list):
                 def _check(entry):
-                    if isinstance(entry, six.string_types):
+                    if isinstance(entry, (str, )):
                         return self._interpolate(key, entry)
                     return entry
                 new = [_check(entry) for entry in val]
@@ -534,7 +533,7 @@ def __setitem__(self, key, value, unrepr=False):
         ``unrepr`` must be set when setting a value to a dictionary, without
         creating a new sub-section.
         """
-        if not isinstance(key, six.string_types):
+        if not isinstance(key, (str, )):
             raise ValueError('The key "%s" is not a string.' % key)
 
         # add the comment
@@ -568,11 +567,11 @@ def __setitem__(self, key, value, unrepr=False):
             if key not in self:
                 self.scalars.append(key)
             if not self.main.stringify:
-                if isinstance(value, six.string_types):
+                if isinstance(value, (str, )):
                     pass
                 elif isinstance(value, (list, tuple)):
                     for entry in value:
-                        if not isinstance(entry, six.string_types):
+                        if not isinstance(entry, (str, )):
                             raise TypeError('Value is not a string "%s".' % entry)
                 else:
                     raise TypeError('Value is not a string "%s".' % value)
@@ -920,7 +919,7 @@ def as_bool(self, key):
             return False
         else:
             try:
-                if not isinstance(val, six.string_types):
+                if not isinstance(val, (str, )):
                     # TODO: Why do we raise a KeyError here?
                     raise KeyError()
                 else:
@@ -1210,7 +1209,7 @@ def _load(self, infile, configspec):
         except AttributeError:
             pass
 
-        if isinstance(infile, six.string_types):
+        if isinstance(infile, (str, )):
             self.filename = infile
             if os.path.isfile(infile):
                 with open(infile, 'rb') as h:
@@ -1278,7 +1277,7 @@ def set_section(in_section, this_section):
                         break
                 break
 
-        assert all(isinstance(line, six.string_types) for line in content), repr(content)
+        assert all(isinstance(line, (str, )) for line in content), repr(content)
         content = [line.rstrip('\r\n') for line in content]
 
         self._parse(content)
@@ -1387,7 +1386,7 @@ def _handle_bom(self, infile):
         else:
             line = infile
 
-        if isinstance(line, six.text_type):
+        if isinstance(line, str):
             # it's already decoded and there's no need to do anything
             # else, just use the _decode utility method to handle
             # listifying appropriately
@@ -1432,7 +1431,7 @@ def _handle_bom(self, infile):
 
         # No encoding specified - so we need to check for UTF8/UTF16
         for BOM, (encoding, final_encoding) in list(BOMS.items()):
-            if not isinstance(line, six.binary_type) or not line.startswith(BOM):
+            if not isinstance(line, bytes) or not line.startswith(BOM):
                 # didn't specify a BOM, or it's not a bytestring
                 continue
             else:
@@ -1448,9 +1447,9 @@ def _handle_bom(self, infile):
                     else:
                         infile = newline
                     # UTF-8
-                    if isinstance(infile, six.text_type):
+                    if isinstance(infile, str):
                         return infile.splitlines(True)
-                    elif isinstance(infile, six.binary_type):
+                    elif isinstance(infile, bytes):
                         return infile.decode('utf-8').splitlines(True)
                     else:
                         return self._decode(infile, 'utf-8')
@@ -1458,12 +1457,8 @@ def _handle_bom(self, infile):
                 return self._decode(infile, encoding)
 
 
-        if six.PY2 and isinstance(line, str):
-            # don't actually do any decoding, since we're on python 2 and
-            # returning a bytestring is fine
-            return self._decode(infile, None)
         # No BOM discovered and no encoding specified, default to UTF-8
-        if isinstance(infile, six.binary_type):
+        if isinstance(infile, bytes):
             return infile.decode('utf-8').splitlines(True)
         else:
             return self._decode(infile, 'utf-8')
@@ -1475,18 +1470,18 @@ def _decode(self, infile, encoding):
 
         if is a string, it also needs converting to a list.
         """
-        if isinstance(infile, six.binary_type):
+        if isinstance(infile, bytes):
             # NOTE: Could raise a ``UnicodeDecodeError``
             if encoding:
                 return infile.decode(encoding).splitlines(True)
             else:
                 return infile.splitlines(True)
-        if isinstance(infile, six.string_types):
+        if isinstance(infile, (str, )):
             return infile.splitlines(True)
 
         if encoding:
             for i, line in enumerate(infile):
-                if isinstance(line, six.binary_type):
+                if isinstance(line, bytes):
                     # NOTE: The isinstance test here handles mixed lists of unicode/string
                     # NOTE: But the decode will break on any non-string values
                     # NOTE: Or could raise a ``UnicodeDecodeError``
@@ -1496,7 +1491,7 @@ def _decode(self, infile, encoding):
 
     def _decode_element(self, line):
         """Decode element to unicode if necessary."""
-        if isinstance(line, six.binary_type) and self.default_encoding:
+        if isinstance(line, bytes) and self.default_encoding:
             return line.decode(self.default_encoding)
         else:
             return line
@@ -1508,7 +1503,7 @@ def _str(self, value):
         Used by ``stringify`` within validate, to turn non-string values
         into strings.
         """
-        if not isinstance(value, six.string_types):
+        if not isinstance(value, (str, )):
             # intentionally 'str' because it's just whatever the "normal"
             # string type is for the python version we're dealing with
             return str(value)
@@ -1761,7 +1756,7 @@ def _quote(self, value, multiline=True):
                 return self._quote(value[0], multiline=False) + ','
             return ', '.join([self._quote(val, multiline=False)
                 for val in value])
-        if not isinstance(value, six.string_types):
+        if not isinstance(value, (str, )):
             if self.stringify:
                 # intentionally 'str' because it's just whatever the "normal"
                 # string type is for the python version we're dealing with
@@ -2081,7 +2076,7 @@ def write(self, outfile=None, section=None):
         if not output.endswith(newline):
             output += newline
 
-        if isinstance(output, six.binary_type):
+        if isinstance(output, bytes):
             output_bytes = output
         else:
             output_bytes = output.encode(self.encoding or
@@ -2323,7 +2318,7 @@ def reload(self):
         This method raises a ``ReloadError`` if the ConfigObj doesn't have
         a filename attribute pointing to a file.
         """
-        if not isinstance(self.filename, six.string_types):
+        if not isinstance(self.filename, (str, )):
             raise ReloadError()
 
         filename = self.filename
diff --git a/src/configobj/validate.py b/src/configobj/validate.py
index 5775aed..25b8779 100644
--- a/src/configobj/validate.py
+++ b/src/configobj/validate.py
@@ -167,22 +167,6 @@
 )
 
 
-#TODO - #21 - six is part of the repo now, but we didn't switch over to it here
-# this could be replaced if six is used for compatibility, or there are no
-# more assertions about items being a string
-if sys.version_info < (3,):
-    string_type = basestring
-else:
-    string_type = str
-    # so tests that care about unicode on 2.x can specify unicode, and the same
-    # tests when run on 3.x won't complain about a undefined name "unicode"
-    # since all strings are unicode on 3.x we just want to pass it through
-    # unchanged
-    unicode = lambda x: x
-    # in python 3, all ints are equivalent to python 2 longs, and they'll
-    # never show "L" in the repr
-    long = int
-
 _list_arg = re.compile(r'''
     (?:
         ([a-zA-Z_][a-zA-Z0-9_]*)\s*=\s*list\(
@@ -284,22 +268,22 @@ def dottedQuadToNum(ip):
 
 def numToDottedQuad(num):
     """
-    Convert int or long int to dotted quad string
+    Convert int int to dotted quad string
 
-    >>> numToDottedQuad(long(-1))
+    >>> numToDottedQuad(int(-1))
     Traceback (most recent call last):
     ValueError: Not a good numeric IP: -1
-    >>> numToDottedQuad(long(1))
+    >>> numToDottedQuad(int(1))
     '0.0.0.1'
-    >>> numToDottedQuad(long(16777218))
+    >>> numToDottedQuad(int(16777218))
     '1.0.0.2'
-    >>> numToDottedQuad(long(16908291))
+    >>> numToDottedQuad(int(16908291))
     '1.2.0.3'
-    >>> numToDottedQuad(long(16909060))
+    >>> numToDottedQuad(int(16909060))
     '1.2.3.4'
-    >>> numToDottedQuad(long(4294967295))
+    >>> numToDottedQuad(int(4294967295))
     '255.255.255.255'
-    >>> numToDottedQuad(long(4294967296))
+    >>> numToDottedQuad(int(4294967296))
     Traceback (most recent call last):
     ValueError: Not a good numeric IP: 4294967296
     >>> numToDottedQuad(-1)
@@ -325,11 +309,11 @@ def numToDottedQuad(num):
     import socket, struct
 
     # no need to intercept here, 4294967295L is fine
-    if num > long(4294967295) or num < 0:
+    if num > int(4294967295) or num < 0:
         raise ValueError('Not a good numeric IP: %s' % num)
     try:
         return socket.inet_ntoa(
-            struct.pack('!L', long(num)))
+            struct.pack('!L', int(num)))
     except (socket.error, struct.error, OverflowError):
         raise ValueError('Not a good numeric IP: %s' % num)
 
@@ -481,9 +465,9 @@ class Validator(object):
     ...     # check that value is of the correct type.
     ...     # possible valid inputs are integers or strings
     ...     # that represent integers
-    ...     if not isinstance(value, (int, long, string_type)):
+    ...     if not isinstance(value, (int, str)):
     ...         raise VdtTypeError(value)
-    ...     elif isinstance(value, string_type):
+    ...     elif isinstance(value, str):
     ...         # if we are given a string
     ...         # attempt to convert to an integer
     ...         try:
@@ -754,7 +738,7 @@ def _is_num_param(names, values, to_float=False):
     for (name, val) in zip(names, values):
         if val is None:
             out_params.append(val)
-        elif isinstance(val, (int, long, float, string_type)):
+        elif isinstance(val, (int, float, str)):
             try:
                 out_params.append(fun(val))
             except ValueError:
@@ -772,7 +756,7 @@ def _is_num_param(names, values, to_float=False):
 
 def is_integer(value, min=None, max=None):
     """
-    A check that tests that a given value is an integer (int, or long)
+    A check that tests that a given value is an integer (int)
     and optionally, between bounds. A negative value is accepted, while
     a float will fail.
 
@@ -812,9 +796,9 @@ def is_integer(value, min=None, max=None):
     """
     (min_val, max_val) = _is_num_param(  # pylint: disable=unbalanced-tuple-unpacking
         ('min', 'max'), (min, max))
-    if not isinstance(value, (int, long, string_type)):
+    if not isinstance(value, (int, str)):
         raise VdtTypeError(value)
-    if isinstance(value, string_type):
+    if isinstance(value, str):
         # if it's a string - does it represent an integer ?
         try:
             value = int(value)
@@ -864,7 +848,7 @@ def is_float(value, min=None, max=None):
     """
     (min_val, max_val) = _is_num_param(  # pylint: disable=unbalanced-tuple-unpacking
         ('min', 'max'), (min, max), to_float=True)
-    if not isinstance(value, (int, long, float, string_type)):
+    if not isinstance(value, (int, float, str)):
         raise VdtTypeError(value)
     if not isinstance(value, float):
         # if it's a string - does it represent a float ?
@@ -929,7 +913,7 @@ def is_boolean(value):
     VdtTypeError: the value "up" is of the wrong type.
 
     """
-    if isinstance(value, string_type):
+    if isinstance(value, str):
         try:
             return bool_dict[value.lower()]
         except KeyError:
@@ -972,7 +956,7 @@ def is_ip_addr(value):
     Traceback (most recent call last):
     VdtTypeError: the value "0" is of the wrong type.
     """
-    if not isinstance(value, string_type):
+    if not isinstance(value, str):
         raise VdtTypeError(value)
     value = value.strip()
     try:
@@ -1015,7 +999,7 @@ def is_list(value, min=None, max=None):
     """
     (min_len, max_len) = _is_num_param(  # pylint: disable=unbalanced-tuple-unpacking
         ('min', 'max'), (min, max))
-    if isinstance(value, string_type):
+    if isinstance(value, str):
         raise VdtTypeError(value)
     try:
         num_members = len(value)
@@ -1084,7 +1068,7 @@ def is_string(value, min=None, max=None):
     Traceback (most recent call last):
     VdtValueTooLongError: the value "1234" is too long.
     """
-    if not isinstance(value, string_type):
+    if not isinstance(value, str):
         raise VdtTypeError(value)
     (min_len, max_len) = _is_num_param(  # pylint: disable=unbalanced-tuple-unpacking
         ('min', 'max'), (min, max))
@@ -1191,7 +1175,7 @@ def is_string_list(value, min=None, max=None):
     Traceback (most recent call last):
     VdtTypeError: the value "hello" is of the wrong type.
     """
-    if isinstance(value, string_type):
+    if isinstance(value, str):
         raise VdtTypeError(value)
     return [is_string(mem) for mem in is_list(value, min, max)]
 
@@ -1326,7 +1310,7 @@ def is_option(value, *options):
     Traceback (most recent call last):
     VdtTypeError: the value "0" is of the wrong type.
     """
-    if not isinstance(value, string_type):
+    if not isinstance(value, str):
         raise VdtTypeError(value)
     if not value in options:
         raise VdtValueError(value)
@@ -1398,15 +1382,15 @@ def _test(value, *args, **keywargs):
     >>> v.check('pass(default=list(1, 2, 3, 4))', None, True)
     ['1', '2', '3', '4']
 
-    Bug test for unicode arguments
+    Bug test for str arguments
     >>> v = Validator()
-    >>> v.check(unicode('string(min=4)'), unicode('test')) == unicode('test')
+    >>> v.check('string(min=4)', 'test') == 'test'
     True
 
     >>> v = Validator()
-    >>> v.get_default_value(unicode('string(min=4, default="1234")')) == unicode('1234')
+    >>> v.get_default_value('string(min=4, default="1234")') == '1234'
     True
-    >>> v.check(unicode('string(min=4, default="1234")'), unicode('test')) == unicode('test')
+    >>> v.check('string(min=4, default="1234")', 'test') == 'test'
     True
 
     >>> v = Validator()
diff --git a/src/tests/test_configobj.py b/src/tests/test_configobj.py
index b1f2d01..78af9ed 100644
--- a/src/tests/test_configobj.py
+++ b/src/tests/test_configobj.py
@@ -11,7 +11,7 @@
 from tempfile import NamedTemporaryFile
 
 import pytest
-import six
+import io
 import mock
 
 import configobj as co
@@ -40,13 +40,13 @@ def cfg_lines(config_string_representation):
                          '{!r}'.format(config_string_representation))
 
     first_content = lines[line_no_with_content]
-    if isinstance(first_content, six.binary_type):
+    if isinstance(first_content, bytes):
         first_content = first_content.decode('utf-8')
     ws_chars = len(re.search(r'^(\s*)', first_content).group(1))
 
     def yield_stringified_line():
         for line in lines:
-            if isinstance(line, six.binary_type):
+            if isinstance(line, bytes):
                 yield line.decode('utf-8')
             else:
                 yield line
@@ -74,7 +74,7 @@ def make_file_with_contents_and_return_name(config_string_representation):
 
         with NamedTemporaryFile(delete=False, mode='wb') as cfg_file:
             for line in lines:
-                if isinstance(line, six.binary_type):
+                if isinstance(line, bytes):
                     cfg_file.write(line + os.linesep.encode('utf-8'))
                 else:
                     cfg_file.write((line + os.linesep).encode('utf-8'))
@@ -191,11 +191,7 @@ def test_unicode_conversion_when_encoding_is_set(self, cfg_contents):
 
         c = ConfigObj(cfg, encoding='utf8')
 
-        if six.PY2:
-            assert not isinstance(c['test'], str)
-            assert isinstance(c['test'], unicode)
-        else:
-            assert isinstance(c['test'], str)
+        assert isinstance(c['test'], str)
 
 
     #issue #18
@@ -203,11 +199,7 @@ def test_no_unicode_conversion_when_encoding_is_omitted(self, cfg_contents):
         cfg = cfg_contents(b"test = some string")
 
         c = ConfigObj(cfg)
-        if six.PY2:
-            assert isinstance(c['test'], str)
-            assert not isinstance(c['test'], unicode)
-        else:
-            assert isinstance(c['test'], str)
+        assert isinstance(c['test'], str)
 
     #issue #44
     def test_that_encoding_using_list_of_strings(self):
@@ -215,11 +207,7 @@ def test_that_encoding_using_list_of_strings(self):
 
         c = ConfigObj(cfg, encoding='utf8')
 
-        if six.PY2:
-            assert isinstance(c['test'], unicode)
-            assert not isinstance(c['test'], str)
-        else:
-            assert isinstance(c['test'], str)
+        assert isinstance(c['test'], str)
 
         assert c['test'] == '\U0001f41c'
 
@@ -228,7 +216,7 @@ def test_encoding_in_subsections(self, ant_cfg, cfg_contents):
         c = cfg_contents(ant_cfg)
         cfg = ConfigObj(c, encoding='utf-8')
 
-        assert isinstance(cfg['tags']['bug']['translated'], six.text_type)
+        assert isinstance(cfg['tags']['bug']['translated'], str)
 
     #issue #44 and #55
     def test_encoding_in_config_files(self, request, ant_cfg):
@@ -238,7 +226,7 @@ def test_encoding_in_config_files(self, request, ant_cfg):
         request.addfinalizer(lambda : os.unlink(cfg_file.name))
 
         cfg = ConfigObj(cfg_file.name, encoding='utf-8')
-        assert isinstance(cfg['tags']['bug']['translated'], six.text_type)
+        assert isinstance(cfg['tags']['bug']['translated'], str)
         cfg.write()
 
     def test_encoding_from_filelike(self):
@@ -248,7 +236,7 @@ def test_encoding_from_filelike(self):
         c = ConfigObj(stream, encoding='utf-8')
         text = c['text']
 
-        assert isinstance(text, unicode if six.PY2 else str)
+        assert isinstance(text, str)
         assert text == '\u00a7'
 
 
@@ -516,7 +504,7 @@ def test_unicode_handling():
                   'section': {'test': 'test', 'test2': 'test2'}}
     uc = ConfigObj(u, encoding='utf_8', default_encoding='latin-1')
     assert uc.BOM
-    assert isinstance(uc['test1'], six.text_type)
+    assert isinstance(uc['test1'], str)
     assert uc.encoding == 'utf_8'
     assert uc.newlines == '\n'
     assert len(uc.write()) == 13
@@ -524,14 +512,14 @@ def test_unicode_handling():
     a_list = uc.write()
     assert 'latin1' in str(a_list)
     assert len(a_list) == 14
-    assert isinstance(a_list[0], six.binary_type)
+    assert isinstance(a_list[0], bytes)
     assert a_list[0].startswith(BOM_UTF8)
 
     u = u_base.replace('\n', '\r\n').encode('utf-8').splitlines(True)
     uc = ConfigObj(u)
     assert uc.newlines == '\r\n'
     uc.newlines = '\r'
-    file_like = six.BytesIO()
+    file_like = io.BytesIO()
     uc.write(file_like)
     file_like.seek(0)
     uc2 = ConfigObj(file_like)
@@ -739,7 +727,7 @@ def transform(section, key):
                 val = section[key]
                 newkey = key.replace('XXXX', 'CLIENT1')
                 section.rename(key, newkey)
-                if isinstance(val, six.string_types):
+                if isinstance(val, (str, )):
                     val = val.replace('XXXX', 'CLIENT1')
                     section[newkey] = val
 
@@ -827,7 +815,7 @@ def reloadable_cfg_content(self):
         return content
 
     def test_handle_no_filename(self):
-        for bad_args in ([six.BytesIO()], [], [[]]):
+        for bad_args in ([io.BytesIO()], [], [[]]):
             cfg = ConfigObj(*bad_args)
             with pytest.raises(ReloadError) as excinfo:
                 cfg.reload()
@@ -1044,11 +1032,11 @@ def test_triple_quote_newline_roundtrip(self):
         initial_conf['single'] = "single triple '''\n"
         initial_conf['double'] = 'double triple """\n'
 
-        io = six.BytesIO()
-        initial_conf.write(outfile=io)
-        io.seek(0)
+        f = io.BytesIO()
+        initial_conf.write(outfile=f)
+        f.seek(0)
 
-        loaded_conf = ConfigObj(io)
+        loaded_conf = ConfigObj(f)
         assert loaded_conf['single'] == "single triple '''\n"
         assert loaded_conf['double'] == 'double triple """\n'
 
@@ -1380,21 +1368,21 @@ class TestEdgeCasesWhenWritingOut(object):
     def test_newline_terminated(self, empty_cfg):
         empty_cfg.newlines = '\n'
         empty_cfg['a'] = 'b'
-        collector = six.BytesIO()
+        collector = io.BytesIO()
         empty_cfg.write(collector)
         assert collector.getvalue() == b'a = b\n'
 
     def test_hash_escaping(self, empty_cfg):
         empty_cfg.newlines = '\n'
         empty_cfg['#a'] = 'b # something'
-        collector = six.BytesIO()
+        collector = io.BytesIO()
         empty_cfg.write(collector)
         assert collector.getvalue() == b'"#a" = "b # something"\n'
 
         empty_cfg = ConfigObj()
         empty_cfg.newlines = '\n'
         empty_cfg['a'] = 'b # something', 'c # something'
-        collector = six.BytesIO()
+        collector = io.BytesIO()
         empty_cfg.write(collector)
         assert collector.getvalue() == b'a = "b # something", "c # something"\n'
 
diff --git a/tox.ini b/tox.ini
index 1610a48..12a1d16 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,7 +5,6 @@ envlist = py27, py34, py35, py36, py37
 
 [testenv]
 deps =
-    six
     mock
     pytest
     pytest-cov