Catholic Encyclopedia: Old Catholics
- Practically a list of grievances of (Roman) Catholics in Germany. Dismisses Mathew's London following as "not a matter of any importance."
- http://www.newadvent.org/cathen/11235b.htm

Columbia Encyclopedia: Old Catholics
- Short historical essay.
- http://www.bartleby.com/65/ol/OldCatho.html

Old Roman Catholics
- Part of the Religious Movements Homepage. Written by a college student in a sociology of religion course. Historical and doctrinal profile of Old Catholics, and a bibliography.
- http://religiousmovements.lib.virginia.edu/nrms/Oldcath.html

American Catholic Union
- Association of Old Catholic priests.
- http://www.am-cath.org/