diff --git a/requests/types.py b/requests/types.py
index ebddfb4a..4b609867 100644
--- a/requests/types.py
+++ b/requests/types.py
@@ -64,3 +64,7 @@ Verify = Union[None, bool, Text]
 Cert = Union[Text, Tuple[Text, Text]]
 JSON = Optional[MutableMapping]
 Help = Dict
+Host = str
+Sequence = List
+Filename = str
+KeyValueList = List[Tuple[Text, Text]]
diff --git a/requests/utils.py b/requests/utils.py
index ec831ba0..f477b75e 100644
--- a/requests/utils.py
+++ b/requests/utils.py
@@ -18,12 +18,11 @@ import re
 import socket
 import struct
 import warnings
+import typing
 
 from .__version__ import __version__
 from .import certs
 
-# to_native_string is unused here, but imported here for backwards compatibility
-from ._internal_utils import to_native_string
 from .basics import parse_http_list as _parse_list_header
 from .basics import (
     quote,
@@ -40,7 +39,8 @@ from .basics import (
     getproxies_environment,
 )
 from .cookies import cookiejar_from_dict
-from .structures import CaseInsensitiveDict
+from .structures import HTTPHeaderDict
+from .cookies import RequestsCookieJar
 from .exceptions import (
     InvalidURL, InvalidHeader, FileModeWarning, UnrewindableBodyError
 )
@@ -50,7 +50,7 @@ DEFAULT_CA_BUNDLE_PATH = certs.where()
 if platform.system() == 'Windows':
 
     # provide a proxy_bypass version on Windows without DNS lookups
-    def proxy_bypass_registry(host):
+    def proxy_bypass_registry(host: str) -> bool:
         import winreg
 
         try:
@@ -90,7 +90,7 @@ if platform.system() == 'Windows':
 
         return False
 
-    def proxy_bypass(host):  # noqa
+    def proxy_bypass(host: str) -> bool:  # noqa
         """Return True, if the host should be bypassed.
 
         Checks proxy settings gathered from the environment, if specified,
@@ -103,14 +103,14 @@ if platform.system() == 'Windows':
             return proxy_bypass_registry(host)
 
 
-def dict_to_sequence(d):
+def dict_to_sequence(d: dict) -> typing.List:
     """Returns an internal sequence dictionary update."""
     if hasattr(d, 'items'):
         d = d.items()
     return d
 
 
-def super_len(o):
+def super_len(o) -> int:
     total_length = None
     current_position = 0
     if hasattr(o, '__len__'):
@@ -131,10 +131,10 @@ def super_len(o):
                     (
                         "Requests has determined the content-length for this "
                         "request using the binary size of the file: however, the "
-                        "file has been opened in text mode (i.e. without the 'b' "
+                        "file has been opened in typing.Text mode (i.e. without the 'b' "
                         "flag in the mode). This may lead to an incorrect "
                         "content-length. In Requests 3.0, support will be removed "
-                        "for files in text mode."
+                        "for files in typing.Text mode."
                     ),
                     FileModeWarning,
                 )
@@ -165,7 +165,9 @@ def super_len(o):
     return max(0, total_length - current_position)
 
 
-def get_netrc_auth(url, raise_errors=False):
+def get_netrc_auth(
+    url: str, raise_errors: bool = False
+) -> typing.Tuple[typing.Text, typing.Text]:
     """Returns the Requests tuple auth for a given url from netrc."""
     try:
         from netrc import netrc, NetrcParseError
@@ -213,7 +215,7 @@ def get_netrc_auth(url, raise_errors=False):
         pass
 
 
-def guess_filename(obj):
+def guess_filename(obj) -> str:
     """Tries to guess the filename of the given object."""
     name = getattr(obj, 'name', None)
     if (
@@ -250,7 +252,7 @@ def from_key_val_list(value):
     return collections.OrderedDict(value)
 
 
-def to_key_val_list(value):
+def to_key_val_list(value) -> typing.List[typing.Tuple[typing.Text, typing.Text]]:
     """Take an object and test to see if it can be represented as a
     dictionary. If it can be, return a list of tuples, e.g.,
 
@@ -279,7 +281,7 @@ def to_key_val_list(value):
 
 
 # From mitsuhiko/werkzeug (used with permission).
-def parse_list_header(value):
+def parse_list_header(value: str) -> typing.List[typing.Text]:
     """Parse lists as described by RFC 2068 Section 2.
 
     In particular, parse comma-separated lists where the elements of
@@ -313,7 +315,7 @@ def parse_list_header(value):
 
 
 # From mitsuhiko/werkzeug (used with permission).
-def parse_dict_header(value):
+def parse_dict_header(value) -> dict:
     """Parse lists of key, value pairs as described by RFC 2068 Section 2 and
     convert them into a python dict:
 
@@ -351,7 +353,7 @@ def parse_dict_header(value):
 
 
 # From mitsuhiko/werkzeug (used with permission).
-def unquote_header_value(value, is_filename=False):
+def unquote_header_value(value: str, is_filename: bool = False):
     r"""Unquotes a header value.  (Reversal of :func:`quote_header_value`).
     This does not use the real unquoting but what browsers are actually
     using for quoting.
@@ -376,7 +378,7 @@ def unquote_header_value(value, is_filename=False):
     return value
 
 
-def dict_from_cookiejar(cj):
+def dict_from_cookiejar(cj: RequestsCookieJar) -> dict:
     """Returns a key/value dictionary from a CookieJar.
 
     :param cj: CookieJar object to extract cookies from.
@@ -388,7 +390,9 @@ def dict_from_cookiejar(cj):
     return cookie_dict
 
 
-def add_dict_to_cookiejar(cj, cookie_dict):
+def add_dict_to_cookiejar(
+    cj: RequestsCookieJar, cookie_dict: dict
+) -> RequestsCookieJar:
     """Returns a CookieJar from a key/value dictionary.
 
     :param cj: CookieJar to insert cookies into.
@@ -398,7 +402,7 @@ def add_dict_to_cookiejar(cj, cookie_dict):
     return cookiejar_from_dict(cookie_dict, cj)
 
 
-def get_encodings_from_content(content):
+def get_encodings_from_content(content: str) -> typing.List[str]:
     """Returns encodings from given content string.
 
     :param content: bytestring to extract encodings from.
@@ -423,7 +427,7 @@ def get_encodings_from_content(content):
     )
 
 
-def get_encoding_from_headers(headers):
+def get_encoding_from_headers(headers: typing.MutableMapping) -> str:
     """Returns encodings from given HTTP Header Dict.
 
     :param headers: dictionary to extract encoding from.
@@ -437,7 +441,7 @@ def get_encoding_from_headers(headers):
     if 'charset' in params:
         return params['charset'].strip("'\"")
 
-    if 'text' in content_type:
+    if 'typing.Text' in content_type:
         return 'ISO-8859-1'
 
 
@@ -465,50 +469,13 @@ def iter_slices(string, slice_length):
         pos += slice_length
 
 
-def get_unicode_from_response(r):
-    """Returns the requested content back in unicode.
-
-    :param r: Response object to get unicode content from.
-
-    Tried:
-
-    1. charset from content-type
-    2. fall back and replace all unicode characters
-
-    :rtype: str
-    """
-    warnings.warn(
-        (
-            'In requests 3.0, get_unicode_from_response will be removed. For '
-            'more information, please see the discussion on issue #2266. (This'
-            ' warning should only appear once.)'
-        ),
-        DeprecationWarning,
-    )
-    tried_encodings = []
-    # Try charset from content-type
-    encoding = get_encoding_from_headers(r.headers)
-    if encoding:
-        try:
-            return str(r.content, encoding)
-
-        except UnicodeError:
-            tried_encodings.append(encoding)
-    # Fall back:
-    try:
-        return str(r.content, encoding, errors='replace')
-
-    except TypeError:
-        return r.content
-
-
 # The unreserved URI characters (RFC 3986)
 UNRESERVED_SET = frozenset(
     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" + "0123456789-._~"
 )
 
 
-def unquote_unreserved(uri):
+def unquote_unreserved(uri: str) -> str:
     """Un-escape any percent-escape sequences in a URI that are unreserved
     characters. This leaves all reserved, illegal and non-ASCII bytes encoded.
 
@@ -550,7 +517,7 @@ def unquote_unreserved(uri):
     return base.join(parts)
 
 
-def requote_uri(uri):
+def requote_uri(uri: str) -> str:
     """Re-quote the given URI.
 
     This function passes the given URI through an unquote/quote cycle to
@@ -573,7 +540,7 @@ def requote_uri(uri):
         return quote(uri, safe=safe_without_percent)
 
 
-def address_in_network(ip, net):
+def address_in_network(ip: str, net: str) -> bool:
     """This function allows you to check if an IP belongs to a network subnet
 
     Example: returns True if ip = 192.168.1.1 and net = 192.168.1.0/24
@@ -590,7 +557,7 @@ def address_in_network(ip, net):
     return ( ipaddr & netmask) == ( network & netmask)
 
 
-def dotted_netmask(mask):
+def dotted_netmask(mask: str) -> str:
     """Converts mask from /xx format to xxx.xxx.xxx.xxx
 
     Example: if mask is 24 function returns 255.255.255.0
@@ -601,7 +568,7 @@ def dotted_netmask(mask):
     return socket.inet_ntoa(struct.pack('>I', bits))
 
 
-def is_ipv4_address(string_ip):
+def is_ipv4_address(string_ip: str) -> bool:
     """
     :rtype: bool
     """
@@ -613,7 +580,7 @@ def is_ipv4_address(string_ip):
     return True
 
 
-def is_valid_cidr(string_network):
+def is_valid_cidr(string_network: str) -> bool:
     """
     Very simple check of the cidr format in no_proxy variable.
 
@@ -640,7 +607,7 @@ def is_valid_cidr(string_network):
 
 
 @contextlib.contextmanager
-def set_environ(env_name, value):
+def set_environ(env_name: str, value: typing.Optional[str]) -> None:
     """Set the environment variable 'env_name' to 'value'
 
     Save previous value, yield, and then restore the previous value stored in
@@ -662,7 +629,7 @@ def set_environ(env_name, value):
                 os.environ[env_name] = old_value
 
 
-def should_bypass_proxies(url, no_proxy):
+def should_bypass_proxies(url: str, no_proxy: bool) -> bool:
     """
     Returns whether we should bypass proxies or not.
 
@@ -706,7 +673,9 @@ def should_bypass_proxies(url, no_proxy):
         return bool(proxy_bypass(netloc))
 
 
-def get_environ_proxies(url, no_proxy=None):
+def get_environ_proxies(
+    url: str, no_proxy: typing.Optional[bool] = None
+) -> dict:
     """
     Return a dict of environment proxies.
 
@@ -719,7 +688,7 @@ def get_environ_proxies(url, no_proxy=None):
         return getproxies()
 
 
-def select_proxy(url, proxies):
+def select_proxy(url: str, proxies: typing.Optional[typing.MutableMapping[typing.Text, typing.Text]]):
     """Select a proxy for the url, if applicable.
 
     :param url: The url being for the request
@@ -745,7 +714,7 @@ def select_proxy(url, proxies):
     return proxy
 
 
-def default_user_agent(name="python-requests"):
+def default_user_agent(name: str = "python-requests") -> str:
     """
     Return a string representing the default user agent.
 
@@ -754,11 +723,11 @@ def default_user_agent(name="python-requests"):
     return '%s/%s' % (name, __version__)
 
 
-def default_headers():
+def default_headers() -> HTTPHeaderDict:
     """
-    :rtype: requests.structures.CaseInsensitiveDict
+    :rtype: requests.structures.HTTPHeaderDict
     """
-    return CaseInsensitiveDict(
+    return HTTPHeaderDict(
         {
             'User-Agent': default_user_agent(),
             'Accept-Encoding': ', '.join(('gzip', 'deflate')),
@@ -768,7 +737,7 @@ def default_headers():
     )
 
 
-def parse_header_links(value):
+def parse_header_links(value: str) -> typing.List[typing.MutableMapping]:
     """Return a list of parsed link headers proxies.
 
     i.e. Link: <http:/.../front.jpeg>; rel=front; type="image/jpeg",<http://.../back.jpeg>; rel=back;type="image/jpeg"
@@ -798,7 +767,7 @@ def parse_header_links(value):
     return links
 
 
-def is_valid_location(response):
+def is_valid_location(response: 'Response') -> bool:
     """Verify that multiple Location headers weren't
     returned from the last response.
     """
@@ -818,7 +787,7 @@ _null2 = _null * 2
 _null3 = _null * 3
 
 
-def guess_json_utf(data):
+def guess_json_utf(data: bytes) -> typing.Optional[str]:
     """
     :rtype: str
     """
@@ -858,7 +827,7 @@ def guess_json_utf(data):
     return None
 
 
-def prepend_scheme_if_needed(url, new_scheme):
+def prepend_scheme_if_needed(url: str, new_scheme: str) -> str:
     """Given a URL that may or may not have a scheme, prepend the given scheme.
     Does not replace a present scheme with the one provided as an argument.
 
@@ -873,7 +842,7 @@ def prepend_scheme_if_needed(url, new_scheme):
     return urlunparse((scheme, netloc, path, params, query, fragment))
 
 
-def get_auth_from_url(url):
+def get_auth_from_url(url: str) -> typing.Tuple[typing.Text, typing.Text]:
     """Given a url with authentication components, extract them into a tuple of
     username,password.
 
@@ -892,7 +861,7 @@ _CLEAN_HEADER_REGEX_BYTE = re.compile(b'^\\S[^\\r\\n]*$|^$')
 _CLEAN_HEADER_REGEX_STR = re.compile(r'^\S[^\r\n]*$|^$')
 
 
-def check_header_validity(header):
+def check_header_validity(header: typing.Tuple[typing.Text, typing.Text]) -> None:
     """Verifies that header value is a string which doesn't contain
     leading whitespace or return characters. This prevents unintended
     header injection.
@@ -918,7 +887,7 @@ def check_header_validity(header):
         )
 
 
-def urldefragauth(url):
+def urldefragauth(url: str) -> str:
     """
     Given a url remove the fragment and the authentication part.
 
@@ -932,7 +901,7 @@ def urldefragauth(url):
     return urlunparse((scheme, netloc, path, params, query, ''))
 
 
-def rewind_body(prepared_request):
+def rewind_body(prepared_request: 'PreparedRequest') -> None:
     """Move file pointer back to its recorded starting position
     so it can be read again on redirect.
     """
@@ -954,7 +923,7 @@ def rewind_body(prepared_request):
         )
 
 
-def is_stream(data):
+def is_stream(data: bytes) -> bool:
     """Given data, determines if it should be sent as a stream."""
     is_iterable = getattr(data, '__iter__', False)
     is_io_type = not isinstance(