Britannica Online
Encyclopedia Britannica is the world’s most comprehensive reference product, a distinction it has held since its first publication in 1768.

Infoplease
Containing nearly 51,000 entries (marshalling six and one-half million words on a vast range of topics), and with more than 80,000 hypertext cross-references, Columbia Encyclopedia, Sixth Edition is among the most complete and up-to-date encyclopedias ever produced.

Encyclopedia.com
The Internet’s premiere, free encyclopedia provides users with more than 57,000 frequently updated articles from the Columbia Encyclopedia, Sixth Edition. Each article is enhanced with links to newspaper and magazine articles as well as pictures and maps – all provided by HighBeam Research.

Wikipedia
Welcome to Wikipedia! We are building an open-content encyclopedia in many languages. In the English version, started in January 2001, Wikipedia is now working on 278,347 articles. Learn how to edit pages, experiment in the sandbox and visit the Community Portal to find out how you can participate in the development of Wikipedia.