Catholic Encyclopedia: Online version of the classic 1913 encyclopedia explaining Catholic doctrines, past and present. Complete text of all articles.
Catholic Encyclopedia: The complete Catholic Encyclopedia (1917 Edition) online.
Jacques Maritain Center Art Gallery: Color illustrations from the Catholic Encyclopedia.
Wikipedia: Catholic Encyclopedia: An article which talks about the history of the Catholic Encyclopedia published in 1913 and the New Catholic Encyclopedia, which was first published in 1967.