diff --git a/.circleci/config.yml b/.circleci/config.yml
new file mode 100644
index 0000000..2df94b6
--- /dev/null
+++ b/.circleci/config.yml
@@ -0,0 +1,82 @@
+version: 2.1
+
+orbs:
+  win: circleci/windows@1.0.0
+
+workflows:
+  workflow:
+    jobs:
+      - go-build:
+          name: Go 1.14
+          docker-image: circleci/golang:1.14
+          build-as-module: true
+      - go-build:
+          name: Go 1.13
+          docker-image: circleci/golang:1.13
+          build-as-module: true
+      - go-build:
+          name: Go 1.12
+          docker-image: circleci/golang:1.12
+      - go-build:
+          name: Go 1.11
+          docker-image: circleci/golang:1.11
+      - go-build:
+          name: Go 1.10
+          docker-image: circleci/golang:1.10
+      - go-build:
+          name: Go 1.9
+          docker-image: circleci/golang:1.9
+      - go-build:
+          name: Go 1.8
+          docker-image: circleci/golang:1.8
+      - go-build-windows:
+          name: Windows
+
+jobs:
+  go-build:
+    parameters:
+      docker-image:
+        type: string
+      build-as-module:
+        type: boolean
+        default: false
+
+    docker:
+      - image: <<parameters.docker-image>>
+
+    working_directory: /go/src/github.com/launchdarkly/go-ntlm-proxy-auth
+
+    steps:
+      - checkout
+
+      - unless:
+          condition: <<parameters.build-as-module>>
+          steps:
+            - run: go get -t .
+      
+      - run: go build
+
+  go-build-windows:
+    executor:
+      name: win/vs2019
+      shell: powershell.exe
+
+    environment:
+      GOPATH: C:\Users\VssAdministrator\go
+      PACKAGE_PATH: github.com/launchdarkly/go-ntlm-proxy-auth
+
+    steps:
+      - checkout
+      - run: go version
+      - run:
+          name: move source
+          command: |
+            go env GOPATH
+            mkdir ${env:GOPATH}\src\${env:PACKAGE_PATH}
+            mv * ${env:GOPATH}\src\${env:PACKAGE_PATH}
+      - run:
+          name: build and test
+          command: |
+            cd ${env:GOPATH}\src\${env:PACKAGE_PATH}
+            go get -t .
+            go test -v -race ./...
diff --git a/README.md b/README.md
index 3dc562c..f0c9bf7 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,7 @@
 
 [![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
 [![GoDoc](https://godoc.org/github.com/launchdarkly/go-ntlm-proxy-auth?status.svg)](https://godoc.org/github.com/launchdarkly/go-ntlm-proxy-auth)
+[![Circle CI](https://circleci.com/gh/launchdarkly/go-ntlm-proxy-auth.svg?style=svg)](https://circleci.com/gh/launchdarkly/go-ntlm-proxy-auth)
 
 With this package, you can connect to http/https servers protected by an NTLM proxy in Golang.
 
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..cdb0ee5
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,8 @@
+module github.com/launchdarkly/go-ntlm-proxy-auth
+
+go 1.13
+
+require (
+	github.com/launchdarkly/go-ntlmssp v0.0.0-20190601005913-a22bdd33b2a4
+	golang.org/x/crypto v0.0.0-20200604202706-70a84ac30bf9 // indirect
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..e2c63e9
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,9 @@
+github.com/launchdarkly/go-ntlmssp v0.0.0-20190601005913-a22bdd33b2a4 h1:r1FdPJK3SrnEKWrE8M1C57lxywsXTOdDTw8+cBaIhTI=
+github.com/launchdarkly/go-ntlmssp v0.0.0-20190601005913-a22bdd33b2a4/go.mod h1:rZQicBRNZBfM+eydZ8LNaQ0p9twUfP6T0hUzJFhaxM4=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20200604202706-70a84ac30bf9 h1:vEg9joUBmeBcK9iSJftGNf3coIG4HqZElCPehJsfAYM=
+golang.org/x/crypto v0.0.0-20200604202706-70a84ac30bf9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=