diff --git a/github/AuthenticatedUser.py b/github/AuthenticatedUser.py
index 2f0b07a5..adb94d39 100644
--- a/github/AuthenticatedUser.py
+++ b/github/AuthenticatedUser.py
@@ -55,6 +55,8 @@ import github.Event
 import github.Authorization
 import github.Notification
 
+import Consts
+
 
 class AuthenticatedUser(github.GithubObject.CompletableGithubObject):
     """
@@ -446,7 +448,7 @@ class AuthenticatedUser(github.GithubObject.CompletableGithubObject):
         if client_secret is not github.GithubObject.NotSet:
             post_parameters["client_secret"] = client_secret
         if onetime_password is not None:
-            request_header = {'X-GitHub-OTP': onetime_password}  # pragma no cover (Should be covered)
+            request_header = {Consts.headerOTP: onetime_password}  # pragma no cover (Should be covered)
         else:
             request_header = None
         headers, data = self._requester.requestJsonAndCheck(
diff --git a/github/CommitComment.py b/github/CommitComment.py
index 99ab9d5c..d5224a11 100644
--- a/github/CommitComment.py
+++ b/github/CommitComment.py
@@ -33,9 +33,10 @@
 ################################################################################
 
 import github.GithubObject
-
 import github.NamedUser
 
+import Consts
+
 
 class CommitComment(github.GithubObject.CompletableGithubObject):
     """
@@ -171,7 +172,7 @@ class CommitComment(github.GithubObject.CompletableGithubObject):
             self._requester,
             self.url + "/reactions",
             None,
-            headers={'Accept': 'application/vnd.github.squirrel-girl-preview'}
+            headers={'Accept': Consts.mediaTypeReactionsPreview}
         )
 
     def create_reaction(self, reaction_type):
@@ -192,7 +193,7 @@ class CommitComment(github.GithubObject.CompletableGithubObject):
             "POST",
             self.url + "/reactions",
             input=post_parameters,
-            headers={'Accept': 'application/vnd.github.squirrel-girl-preview'}
+            headers={'Accept': Consts.mediaTypeReactionsPreview}
         )
         return github.Reaction.Reaction(self._requester, headers, data, completed=True)
 
diff --git a/github/Consts.py b/github/Consts.py
index c738c6a9..20a75e5f 100644
--- a/github/Consts.py
+++ b/github/Consts.py
@@ -40,3 +40,40 @@ PROCESSING_202_WAIT_TIME = 2
 # ##############################################################################
 RES_ETAG = "etag"
 RES_LAST_MODIFIED = "last-modified"
+
+# Inspired by https://github.com/google/go-github
+
+# Headers
+
+headerRateLimit = "x-ratelimit-limit"
+headerRateRemaining = "x-ratelimit-remaining"
+headerRateReset = "x-ratelimit-reset"
+headerOTP = "X-GitHub-OTP"
+
+defaultMediaType = "application/octet-stream"
+
+# Custom media type for preview API
+
+# https://developer.github.com/changes/2014-12-09-new-attributes-for-stars-api/
+mediaTypeStarringPreview = "application/vnd.github.v3.star+json"
+
+# https://developer.github.com/changes/2016-02-19-source-import-preview-api/
+mediaTypeImportPreview = "application/vnd.github.barred-rock-preview"
+
+# https://developer.github.com/changes/2016-05-12-reactions-api-preview/
+mediaTypeReactionsPreview = "application/vnd.github.squirrel-girl-preview"
+
+# https://developer.github.com/changes/2016-09-14-Integrations-Early-Access/
+mediaTypeIntegrationPreview = "application/vnd.github.machine-man-preview+json"
+
+# https://developer.github.com/changes/2017-01-05-commit-search-api/
+mediaTypeCommitSearchPreview = "application/vnd.github.cloak-preview"
+
+# https://developer.github.com/changes/2017-02-28-user-blocking-apis-and-webhook/
+mediaTypeBlockUsersPreview = "application/vnd.github.giant-sentry-fist-preview+json"
+
+# https://developer.github.com/changes/2017-07-17-update-topics-on-repositories/
+mediaTypeTopicsPreview = "application/vnd.github.mercy-preview+json"
+
+# https://developer.github.com/changes/2018-02-22-label-description-search-preview/
+mediaTypeLabelDescriptionSearchPreview = "application/vnd.github.symmetra-preview+json"
diff --git a/github/Installation.py b/github/Installation.py
index f3f74757..79690d5f 100644
--- a/github/Installation.py
+++ b/github/Installation.py
@@ -39,7 +39,9 @@ import github.Event
 import github.Authorization
 import github.Notification
 
-INTEGRATION_PREVIEW_HEADERS = {"Accept": "application/vnd.github.machine-man-preview+json"}
+import Consts
+
+INTEGRATION_PREVIEW_HEADERS = {"Accept": Consts.mediaTypeIntegrationPreview}
 
 
 class Installation(github.GithubObject.NonCompletableGithubObject):
diff --git a/github/Issue.py b/github/Issue.py
index b415c6f8..f1d96d75 100644
--- a/github/Issue.py
+++ b/github/Issue.py
@@ -56,6 +56,8 @@ import github.IssueComment
 import github.IssuePullRequest
 import github.Reaction
 
+import Consts
+
 
 class Issue(github.GithubObject.CompletableGithubObject):
     """
@@ -465,7 +467,7 @@ class Issue(github.GithubObject.CompletableGithubObject):
             self._requester,
             self.url + "/reactions",
             None,
-            headers={'Accept': 'application/vnd.github.squirrel-girl-preview'}
+            headers={'Accept': Consts.mediaTypeReactionsPreview}
         )
 
     def create_reaction(self, reaction_type):
@@ -485,7 +487,7 @@ class Issue(github.GithubObject.CompletableGithubObject):
             "POST",
             self.url + "/reactions",
             input=post_parameters,
-            headers={'Accept': 'application/vnd.github.squirrel-girl-preview'}
+            headers={'Accept': Consts.mediaTypeReactionsPreview}
         )
         return github.Reaction.Reaction(self._requester, headers, data, completed=True)
 
diff --git a/github/IssueComment.py b/github/IssueComment.py
index cb037fad..dc689c5a 100644
--- a/github/IssueComment.py
+++ b/github/IssueComment.py
@@ -34,9 +34,10 @@
 ################################################################################
 
 import github.GithubObject
-
 import github.NamedUser
 
+import Consts
+
 
 class IssueComment(github.GithubObject.CompletableGithubObject):
     """
@@ -148,7 +149,7 @@ class IssueComment(github.GithubObject.CompletableGithubObject):
             self._requester,
             self.url + "/reactions",
             None,
-            headers={'Accept': 'application/vnd.github.squirrel-girl-preview'}
+            headers={'Accept': Consts.mediaTypeReactionsPreview}
         )
 
     def create_reaction(self, reaction_type):
@@ -169,7 +170,7 @@ class IssueComment(github.GithubObject.CompletableGithubObject):
             "POST",
             self.url + "/reactions",
             input=post_parameters,
-            headers={'Accept': 'application/vnd.github.squirrel-girl-preview'}
+            headers={'Accept': Consts.mediaTypeReactionsPreview}
         )
         return github.Reaction.Reaction(self._requester, headers, data, completed=True)
 
diff --git a/github/Label.py b/github/Label.py
index 08a2d88d..e2efac20 100644
--- a/github/Label.py
+++ b/github/Label.py
@@ -35,6 +35,8 @@ import urllib
 
 import github.GithubObject
 
+import Consts
+
 
 class Label(github.GithubObject.CompletableGithubObject):
     """
@@ -107,7 +109,7 @@ class Label(github.GithubObject.CompletableGithubObject):
             "PATCH",
             self.url,
             input=post_parameters,
-            headers={'Accept': 'application/vnd.github.symmetra-preview+json'}
+            headers={'Accept': Consts.mediaTypeLabelDescriptionSearchPreview}
         )
         self._useAttributes(data)
 
diff --git a/github/MainClass.py b/github/MainClass.py
index 28b57ae7..2437778e 100644
--- a/github/MainClass.py
+++ b/github/MainClass.py
@@ -73,6 +73,8 @@ import InstallationAuthorization
 import GithubException
 import Invitation
 
+import Consts
+
 atLeastPython3 = sys.hexversion >= 0x03000000
 
 DEFAULT_BASE_URL = "https://api.github.com"
@@ -504,7 +506,7 @@ class Github(object):
             "/search/commits",
             url_parameters,
             headers={
-                "Accept": "application/vnd.github.cloak-preview"
+                "Accept": Consts.mediaTypeCommitSearchPreview
             }
         )
 
@@ -721,7 +723,7 @@ class GithubIntegration(object):
             url="/installations/{}/access_tokens".format(installation_id),
             headers={
                 "Authorization": "Bearer {}".format(self.create_jwt()),
-                "Accept": "application/vnd.github.machine-man-preview+json",
+                "Accept": Consts.mediaTypeIntegrationPreview,
                 "User-Agent": "PyGithub/Python"
             },
             body=body
diff --git a/github/PullRequestComment.py b/github/PullRequestComment.py
index d0ce6653..05b438e8 100644
--- a/github/PullRequestComment.py
+++ b/github/PullRequestComment.py
@@ -35,9 +35,9 @@
 ################################################################################
 
 import github.GithubObject
-
 import github.NamedUser
 
+import Consts
 
 class PullRequestComment(github.GithubObject.CompletableGithubObject):
     """
@@ -205,7 +205,7 @@ class PullRequestComment(github.GithubObject.CompletableGithubObject):
             self._requester,
             self.url + "/reactions",
             None,
-            headers={'Accept': 'application/vnd.github.squirrel-girl-preview'}
+            headers={'Accept': Consts.mediaTypeReactionsPreview}
         )
 
     def create_reaction(self, reaction_type):
@@ -226,7 +226,7 @@ class PullRequestComment(github.GithubObject.CompletableGithubObject):
             "POST",
             self.url + "/reactions",
             input=post_parameters,
-            headers={'Accept': 'application/vnd.github.squirrel-girl-preview'}
+            headers={'Accept': Consts.mediaTypeReactionsPreview}
         )
         return github.Reaction.Reaction(self._requester, headers, data, completed=True)
 
diff --git a/github/Reaction.py b/github/Reaction.py
index b84c33b1..994ef755 100644
--- a/github/Reaction.py
+++ b/github/Reaction.py
@@ -25,9 +25,10 @@
 ################################################################################
 
 import github.GithubObject
-
 import github.NamedUser
 
+import Consts
+
 
 class Reaction(github.GithubObject.CompletableGithubObject):
     """
@@ -77,7 +78,7 @@ class Reaction(github.GithubObject.CompletableGithubObject):
         self._requester.requestJsonAndCheck(
             "DELETE",
             self._parentUrl("") + "/reactions/" + str(self.id),
-            headers={'Accept': 'application/vnd.github.squirrel-girl-preview'}
+            headers={'Accept': Consts.mediaTypeReactionsPreview}
         )
 
     def _initAttributes(self):
diff --git a/github/Repository.py b/github/Repository.py
index 0c7bfd45..55d9a7ba 100644
--- a/github/Repository.py
+++ b/github/Repository.py
@@ -123,6 +123,8 @@ import github.StatsParticipation
 import github.StatsPunchCard
 import github.Stargazer
 
+import Consts
+
 atLeastPython3 = sys.hexversion >= 0x03000000
 
 
@@ -1077,7 +1079,7 @@ class Repository(github.GithubObject.CompletableGithubObject):
             "POST",
             self.url + "/labels",
             input=post_parameters,
-            headers={'Accept': 'application/vnd.github.symmetra-preview+json'}
+            headers={'Accept': Consts.mediaTypeLabelDescriptionSearchPreview}
         )
         return github.Label.Label(self._requester, headers, data, completed=True)
 
@@ -1179,7 +1181,7 @@ class Repository(github.GithubObject.CompletableGithubObject):
         if vcs_password is not github.GithubObject.NotSet:
             put_parameters["vcs_password"] = vcs_password
 
-        import_header = {"Accept": "application/vnd.github.barred-rock-preview"}
+        import_header = {"Accept": Consts.mediaTypeImportPreview}
 
         headers, data = self._requester.requestJsonAndCheck(
             "PUT",
@@ -2165,7 +2167,7 @@ class Repository(github.GithubObject.CompletableGithubObject):
         :calls: `GET /repos/:owner/:repo/import <https://developer.github.com/v3/migration/source_imports/#get-import-progress>`_
         :rtype: :class:`github.SourceImport.SourceImport`
         """
-        import_header = {"Accept": "application/vnd.github.barred-rock-preview"}
+        import_header = {"Accept": Consts.mediaTypeImportPreview}
         headers, data = self._requester.requestJsonAndCheck(
             "GET",
             self.url + "/import",
@@ -2198,7 +2200,7 @@ class Repository(github.GithubObject.CompletableGithubObject):
             self._requester,
             self.url + "/stargazers",
             None,
-            headers={'Accept': 'application/vnd.github.v3.star+json'}
+            headers={'Accept': Consts.mediaTypeStarringPreview}
         )
 
     def get_stats_contributors(self):
@@ -2366,7 +2368,7 @@ class Repository(github.GithubObject.CompletableGithubObject):
         headers, data = self._requester.requestJsonAndCheck(
             "GET",
             self.url + "/topics",
-            headers={'Accept': 'application/vnd.github.mercy-preview+json'}
+            headers={'Accept': Consts.mediaTypeTopicsPreview}
         )
         return data['names']
 
@@ -2473,7 +2475,7 @@ class Repository(github.GithubObject.CompletableGithubObject):
         headers, data = self._requester.requestJsonAndCheck(
             "PUT",
             self.url + "/topics",
-            headers={'Accept': 'application/vnd.github.mercy-preview+json'},
+            headers={'Accept': Consts.mediaTypeTopicsPreview},
             input=post_parameters
         )
 
diff --git a/github/Requester.py b/github/Requester.py
index f62d2124..5612eac3 100644
--- a/github/Requester.py
+++ b/github/Requester.py
@@ -289,7 +289,7 @@ class Requester:
     def __createException(self, status, headers, output):
         if status == 401 and output.get("message") == "Bad credentials":
             cls = GithubException.BadCredentialsException
-        elif status == 401 and 'x-github-otp' in headers and re.match(r'.*required.*', headers['x-github-otp']):
+        elif status == 401 and Consts.headerOTP in headers and re.match(r'.*required.*', headers[Consts.headerOTP]):
             cls = GithubException.TwoFactorException  # pragma no cover (Should be covered)
         elif status == 403 and output.get("message").startswith("Missing or invalid User Agent string"):
             cls = GithubException.BadUserAgentException
@@ -340,7 +340,7 @@ class Requester:
                 mime_type = headers["Content-Type"]
             else:
                 guessed_type = mimetypes.guess_type(input)
-                mime_type = guessed_type[0] if guessed_type[0] is not None else "application/octet-stream"
+                mime_type = guessed_type[0] if guessed_type[0] is not None else Consts.defaultMediaType
             f = open(local_path, 'rb')
             return mime_type, f
 
@@ -371,10 +371,10 @@ class Requester:
 
         status, responseHeaders, output = self.__requestRaw(cnx, verb, url, requestHeaders, encoded_input)
 
-        if "x-ratelimit-remaining" in responseHeaders and "x-ratelimit-limit" in responseHeaders:
-            self.rate_limiting = (int(responseHeaders["x-ratelimit-remaining"]), int(responseHeaders["x-ratelimit-limit"]))
-        if "x-ratelimit-reset" in responseHeaders:
-            self.rate_limiting_resettime = int(responseHeaders["x-ratelimit-reset"])
+        if Consts.headerRateRemaining in responseHeaders and Consts.headerRateLimit in responseHeaders:
+            self.rate_limiting = (int(responseHeaders[Consts.headerRateRemaining]), int(responseHeaders[Consts.headerRateLimit]))
+        if Consts.headerRateReset in responseHeaders:
+            self.rate_limiting_resettime = int(responseHeaders[Consts.headerRateReset])
 
         if "x-oauth-scopes" in responseHeaders:
             self.oauth_scopes = responseHeaders["x-oauth-scopes"].split(", ")