Jewish Encyclopedia
This is the unedited and complete 12-volume Jewish Encyclopedia, originally published between 1901-1906 and contains more than 15,00 articles and illustrations. Since it was published over 100 years ago it doesn’t contain modern Jewish History.

Catholic Encyclopedia
Unlike general encyclopedias, the Catholic Encyclopedia includes only information relating to Catholic interests, actions, and doctrines from the Catholic point of view. The work on the Encyclopedia was begun January 1905 and completed April 1914. This site also includes the complete Knox Bible, writings of the Fathers and other works such as the Councils, and Summa Theologiae with the Catholic doctrines, and the Catholic Library including such topics as abortion and euthanasia. In 1922 a supplement to the Encyclopedia was published and is in the public domain and available online. The Encyclopedia was updated (New Catholic Encyclopedia) and first published in 1967 and in 2002 and is available online at some libraries.

Encyclopedia Britannica
You may use this site in a limited fashion but a subscription is required to access the premium edition and the children’s encyclopedia, dictionary, and thesaurus. Also featured on this site are featured blogs, trending articles, news, quizzes, browsing galleries by category, lists, and answers to confusing questions.

Stanford Encyclopedia of Philosophy
This up-to-date reference work includes alphabetized philosophy and related disciplines topics.