diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..e1980f4
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,95 @@
+name: Test
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    runs-on: windows-latest
+    strategy:
+       matrix:
+         include:
+           - platform: 'x86_64'
+           - platform: 'x86'
+             packages: >-
+               coreutils
+               moreutils
+           - platform: 'amd64'
+             packages: |
+               coreutils,
+               moreutils
+       fail-fast: false
+
+    name: 'Test ${{ matrix.platform }}'
+
+    steps:
+    - run: git config --global core.autocrlf input
+
+    - uses: actions/checkout@v2
+
+    - name: Install Cygwin
+      uses: ./
+      with:
+        platform: ${{ matrix.platform }}
+        packages: ${{ matrix.packages }}
+
+    - name: Explicitly running shell
+      run: C:\cygwin\bin\bash -lc "echo 'Explicitly run shell'"
+
+    - name: Single-line inline shell
+      run: echo "Running in $(pwd)"
+      shell: C:\cygwin\bin\bash.exe '{0}'
+
+    - name: Multiline inline shell
+      run: >-
+        echo "Running in $(pwd)" &&
+        true
+      shell: C:\cygwin\bin\bash.exe '{0}'
+
+    - name: Shell script
+      run: C:\cygwin\bin\bash.exe tests/script.sh
+
+    - name: Check requested packages got installed
+      run: C:\cygwin\bin\sponge.exe tmp
+      if: contains(matrix.packages, 'moreutils')
+
+  complex-test:
+    runs-on: windows-latest
+    name: 'Complex Test'
+
+    strategy:
+       matrix:
+         include:
+           - combination: 1
+
+    defaults:
+      run:
+        shell: C:\cygwin\bin\bash.exe --noprofile --norc -o igncr -eo pipefail '{0}'
+
+    steps:
+    - run: git config --global core.autocrlf input
+      shell: pwsh -command ". '{0}'".
+
+    - uses: actions/checkout@v2
+
+    - name: Install Cygwin
+      uses: ./
+
+    - name: Run one
+      run: |
+        echo
+        echo "One"
+        echo
+
+    - name: Run two
+      run: |
+        if [[ '${{ matrix.combination }}' == "${COMBINATION}" ]]; then
+          echo "It's true: ${COMBINATION} satisfied"
+        else
+          exit 1
+        fi
+
+        echo
+        echo "Two"
+        echo
+      env:
+        COMBINATION: 1
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..2bddc47
--- /dev/null
+++ b/README.md
@@ -0,0 +1,79 @@
+Cygwin Install GitHub Action
+============================
+
+This GitHub Action can be used in a workflow to install Cygwin.
+
+e.g.
+
+    - run: git config --global core.autocrlf input
+
+    - uses: actions/checkout@v2
+
+    - uses: cygwin/cygwin-install-action@master
+
+    - run: C:\cygwin\bin\bash.exe tests/script.sh
+
+Please fix my terrible cargo-cult PowerShell.
+
+Parameters
+----------
+
+| Input       | Default | Description
+| ----------- | ------- | -----------
+| platform    | x86_64  | Install the x86 or x86\_64 version of Cygwin.
+| packages    | *none*  | List of additional packages to install.
+
+Line endings
+------------
+
+If you're going to use `actions/checkout` in your workflow, you should
+precede that with
+
+    - run: git config --global core.autocrlf input
+
+to ensure that any shell scripts etc. in your repository don't get checked out
+with `\r\n` line endings (leading to `'\r': command not found` errors).
+
+Likewise, if you have multiple lines of shell script in a YAML block for `run:`
+in your workflow file, the file this is written into on the runner ends up with
+`\r\n` line endings.
+
+You can use `>-` (rather than `|`) to ensure that it doesn't contain any
+newlines.
+
+Alternatively, you can also use:
+
+- `igncr` in the `SHELLOPTS` environment variable
+- invoke `bash` with `-o igncr`
+
+PATH
+----
+
+If you want to ensure that PATH only contains Cygwin executables, and other
+stuff installed in the VM image isn't going to get picked up:
+
+- Set PATH to something like `/usr/bin:$(cygpath ${SYSTEMROOT})/system32` in
+  your shell script
+
+or,
+
+- Put `CYGWIN_NOWINPATH=1` into the environment
+- start a login shell with `bash --login`
+- because the profile script from does `cd ${HOME}`, either:
+  * `cd ${GITHUB_WORKSPACE}` in your shell script, or
+  * prevent the profile script from changing directory by putting
+    `CHERE_INVOKING` into the environment
+
+Symlinks
+--------
+
+Unfortunately, Cygwin's `setup` doesn't (currently) honour
+`CYGWIN=winsymlinks:native` or offer an option to control the kind of symlinks
+created, so some executables (e.g. `python`) are created as Cygwin-style
+symlinks. Since CMD and PowerShell don't understand those symlinks, you cannot
+run those executables directly in a `run:` in your workflow. Execute them via
+`bash` or `env` instead.
+
+[1] The
+[Workflow documentation](https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#exit-codes-and-error-action-preference)
+suggests you should also use bash options `-eo pipefail`, omitted here for clarity
diff --git a/action.yml b/action.yml
new file mode 100644
index 0000000..df71e01
--- /dev/null
+++ b/action.yml
@@ -0,0 +1,61 @@
+name: Install Cygwin Action
+description: GitHub Action to install Cygwin
+
+inputs:
+  platform:
+    description: Platform [x86, x86_64]
+    required: false
+    default: x86_64
+  packages:
+    description: Packages to install
+    required: false
+
+runs:
+  using: "composite"
+  steps:
+    - run: |
+        $platform = '${{ inputs.platform }}'
+        $platform = $platform -replace '^(x64|amd64)$', 'x86_64'
+        $platform = $platform -replace '^i686$', 'x86'
+        # validate that platform is one of the expected values
+        if (($platform -ne 'x86') -and ($platform -ne 'x86_64')) {
+          echo "unknown platform $platform"
+          exit 1
+        }
+        Invoke-WebRequest https://cygwin.com/setup-$platform.exe -OutFile C:\setup.exe
+      shell: powershell
+
+    - run: |
+        $packages = '${{ inputs.packages }}'
+        $pkg_list = $packages.Split('', [System.StringSplitOptions]::RemoveEmptyEntries)
+        $pkg_list = $pkg_list | % { $_.Trim() }
+        $pkg_list = $pkg_list | % { $_.Trim(',') }
+
+        $args = @(
+         '-qgnO',
+         '-s', 'http://mirrors.kernel.org/sourceware/cygwin/',
+         '-l', 'C:\cygwin-packages',
+         # always install to C:\cygwin rather than the platform dependent
+         # default to make everything simpler
+         '-R', 'C:\cygwin'
+        )
+
+        if ($pkg_list.Count -gt 0) {
+          $args += '-P'
+          $args += $pkg_list -Join(',')
+        }
+
+        # because setup is a Windows GUI app, make it part of a pipeline to make
+        # PowerShell wait for it to exit
+        & C:\setup.exe $args | Out-Default
+      shell: powershell
+
+    - run: |
+        echo "C:\cygwin\bin" >> $env:GITHUB_PATH
+        # run login shell to copy skeleton profile files
+        C:\cygwin\bin\bash.exe --login
+      shell: powershell
+
+branding:
+  color: green
+  icon: terminal
diff --git a/tests/script.sh b/tests/script.sh
new file mode 100644
index 0000000..6a272cb
--- /dev/null
+++ b/tests/script.sh
@@ -0,0 +1,4 @@
+#!/usr/bin/sh
+echo ""
+echo "Running a script"
+echo ""