From Gentoo Wiki
- Validated Gentoo repository snapshots in the Gentoo Handbook
- Overview over the new Portage sync system
- Layman - Using 'repos.conf' method in the Layman article
- Overlays user guide
- Repository format — A quick reference to Gentoo ebuild repository (overlay) format.
- Repository mirror and Continuous Integration
- Query repository information in the Portageq article
- Using the gentoo git checkout as your local tree
- Masking installed but unsafe ebuild repositories
- Eselect/Repository — an eselect module for manipulating /etc/portage/repos.conf entries to third party repositories (also known as overlays).