diff --git a/.gitignore b/.gitignore
index e00ae94..92b8891 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 openapi.yaml
 *.swp
 *.pyc
+.mypy_cache
diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..7046a26
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,7 @@
+language: python
+python:
+  - "3.6"
+install:
+  - pip install mypy
+script:
+  - mypy openapi
diff --git a/openapi/__init__.py b/openapi/__init__.py
index decd2fe..4faa103 100644
--- a/openapi/__init__.py
+++ b/openapi/__init__.py
@@ -3,4 +3,4 @@
 # that they may be referenced throughout the schema without issue
 from . import info, servers, paths, general, schemas, components, security
 
-__all__ = [OpenAPI]
+__all__ = ["OpenAPI"]
diff --git a/openapi/general.py b/openapi/general.py
index 04a178e..4ee3440 100644
--- a/openapi/general.py
+++ b/openapi/general.py
@@ -1,3 +1,5 @@
+from typing import List
+
 from .object_base import ObjectBase
 
 class ExternalDocumentation(ObjectBase):
@@ -8,7 +10,7 @@ class ExternalDocumentation(ObjectBase):
     .. _External Documentation Object: https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.1.md#externalDocumentationObject
     """
     __slos__ = ['description','url']
-    required_fields = 'url'
+    required_fields: List[str] = ['url']
 
     def _parse_data(self):
         self.description = self._get('description', str)
@@ -21,7 +23,7 @@ class Reference(ObjectBase):
     .. _Reference Object: https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.1.md#referenceObject
     """
     __slots__ = ['ref'] # can't start a variable name with a $
-    required_fields = ['$ref']
+    required_fields: List[str] = ['$ref']
 
     def _parse_data(self):
         self.ref = self._get('$ref', str)
diff --git a/openapi/info.py b/openapi/info.py
index 7e016a3..11e1a12 100644
--- a/openapi/info.py
+++ b/openapi/info.py
@@ -1,3 +1,5 @@
+from typing import List
+
 from .object_base import ObjectBase
 
 class Info(ObjectBase):
@@ -7,7 +9,7 @@ class Info(ObjectBase):
     .. _the spec: https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.1.md#infoObject
     """
     __slots__ = ['title','description','termsOfService','contact','license','version']
-    required_fields = ['title','version']
+    required_fields: List[str] = ['title','version']
 
     def _parse_data(self):
         """
@@ -43,7 +45,7 @@ class License(ObjectBase):
     .. _here: https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.1.md#license-object
     """
     __slots__ = ['name','url']
-    required_fields = ['name']
+    required_fields: List[str] = ['name']
 
     def _parse_data(self):
         """
diff --git a/openapi/object_base.py b/openapi/object_base.py
index 70ffb44..aebe044 100644
--- a/openapi/object_base.py
+++ b/openapi/object_base.py
@@ -1,3 +1,5 @@
+from typing import List
+
 from .errors import SpecError
 
 class ObjectBase:
@@ -7,7 +9,7 @@ class ObjectBase:
     """
     __slots__ = ['path','raw_element','_accessed_members','strict','extensions',
                  '_root', '_original_ref']
-    required_fields = []
+    required_fields: List[str] = []
 
     def __init__(self, path, raw_element, root):
         """
diff --git a/openapi/openapi.py b/openapi/openapi.py
index 4404004..0cc3cb9 100644
--- a/openapi/openapi.py
+++ b/openapi/openapi.py
@@ -1,3 +1,5 @@
+from typing import List
+
 from .object_base import ObjectBase, Map
 from .errors import ReferenceResolutionError
 
@@ -10,7 +12,7 @@ class OpenAPI(ObjectBase):
     """
     __slots__ = ['openapi','info','servers','paths','components','security','tags',
                  'externalDocs','_operation_map','_security']
-    required_fields=['openapi','info','paths']
+    required_fields: List[str] = ['openapi','info','paths']
 
     def __init__(self, raw_document):
         """
diff --git a/openapi/paths.py b/openapi/paths.py
index aa244a1..928a823 100644
--- a/openapi/paths.py
+++ b/openapi/paths.py
@@ -1,5 +1,6 @@
 import json
 import requests
+from typing import List
 from urllib.parse import urlencode # TODO - this will break in python2
 
 from .errors import SpecError
@@ -48,7 +49,7 @@ class Parameter(ObjectBase):
     __slots__ = ['name','in','in_','description','required','deprecated',
                  'allowEmptyValue','style','explode','allowReserved','schema',
                  'example','examples']
-    required_fields = ['name','in']
+    required_fields: List[str] = ['name','in']
 
 
     def _parse_data(self):
@@ -81,7 +82,7 @@ class Operation(ObjectBase):
     __slots__ = ['tags','summary','description','externalDocs','operationId',
                  'parameters','requestBody','responses','callbacks','deprecated',
                  'security','servers']
-    required_fields = ['responses']
+    required_fields: List[str] = ['responses']
 
     def _parse_data(self):
         """
@@ -252,7 +253,6 @@ class SecurityRequirement(ObjectBase):
     """
     """
     ___slots__ = ['name','types']
-    required_fields=[]
 
     def _parse_data(self):
         """
@@ -280,7 +280,7 @@ class RequestBody(ObjectBase):
     .. _RequestBody: https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.1.md#requestBodyObject
     """
     __slots__ = ['description','content','required']
-    required_fields = ['content']
+    required_fields: List[str] = ['content']
 
     def _parse_data(self):
         """
@@ -300,7 +300,6 @@ class MediaType(ObjectBase):
     .. _MediaType: https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.1.md#mediaTypeObject
     """
     __slots__ = ['schema','example','examples','encoding']
-    required_fields = []
 
     def _parse_data(self):
         """
@@ -323,7 +322,7 @@ class Response(ObjectBase):
     .. _Response Object: https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.1.md#response-object
     """
     __slots__ = ['description','headers','content','links']
-    required_fields = ['description']
+    required_fields: List[str] = ['description']
 
     def _parse_data(self):
         """
diff --git a/openapi/schemas.py b/openapi/schemas.py
index a8ef003..9573be9 100644
--- a/openapi/schemas.py
+++ b/openapi/schemas.py
@@ -1,3 +1,5 @@
+from typing import List
+
 from .object_base import ObjectBase
 from .general import Reference # need this for Model below
 
@@ -14,7 +16,6 @@ class Schema(ObjectBase):
                  'properties','additionalProperties','description','format',
                  'default','nullable','discriminator','readOnly','writeOnly',
                  'xml','externalDocs','example','deprecated','_model_type']
-    required_fields = []
 
     def _parse_data(self):
         """