For the last 10 years, the accepted answer has been correct, as git-flow came bundled in Git for Windows. However, as of v2.51.1.windows.1, this has now been dropped: https://github.com/git-for-windows/git/releases/tag/v2.51.1.windows.1

Instructions in the gitflow-avh repo (i.e. the version included in Git for Windows) point to using Git for Windows, so couldn't be used: https://github.com/petervanderdoes/gitflow-avh/wiki/Installing-on-Windows

Instructions in the original gitflow repo exist and can be adapted to use gitflow-avh, but can be simplified: https://github.com/nvie/gitflow/wiki/Windows#user-content-git-for-windows-previously-msysgit

Below are the steps that I used to set up git-flow tools on top of Git for Windows without them bundled:

1. Clone the repo: git clone [email protected]:petervanderdoes/gitflow-avh.git

2. Open folder: gitflow-avh and run install command from Powershell: contrib\msysgit-install.cmd "C:\Program Files\Git\usr"

3. Test: git flow