All the Qubes code is kept in GIT repositories. We divided the project into several components, each of which has its own separate repository, some of them:
You can browse the repositories [on line via GitWeb](http://git.qubes-os.org/gitweb/). The Qubes official repositories are in the `qubes-rX` directory, where X is release number (1, 2, etc).
Currently the preferred way of contributing to the project is by [sending a patch](/wiki/DevelFaq#Q:HowdoIsubmitapatch) via the project's mailing list (`git format-patch`).