Online resources have the potential to replace bulky reference books. The encyclopedia, a benevolent reference work that covers all branches of knowledge, or one branch of knowledge in an exhaustive manner, has found a home in cyberspace.

Online encyclopedias can complement or supplement the printed reference collection. Here is a roundup of some of the best encyclopedias on the Internet:
 

Britannica.com
Britannica.com includes a portion of the contents of the venerable print edition. You can also simultaneously search for reviews of the 125,000 hand-picked reference sites, related books and current articles from magazines such as Discover, The Economist and Newsweek.

Encyclopedia.com
Offers more than 50,000 articles from The Concise Columbia Electronic Encyclopedia (Third Edition). Encyclopedia.com offers 170,000 links, including cross-referenced articles and other sites. You can also access articles and images from the Electric Library for a fee.

Encarta
This free encyclopedia from Microsoft contains 17,000 articles and more than 2,200 photos, illustrations, maps, charts and tables. You can also access the World Atlas and the World English Dictionary, a "talking dictionary" replete with audio files.

Fact Monster
Search 57,000 articles from the Columbia Encyclopedia, Sixth Edition. Simply enter your search term and start reading!
 

Don't overlook "subject encyclopedias" that are devoted to a field or a discipline. Here are a few examples:
 

Encyclopedia Smithsonian
Find easy-to-read articles on Smithsonian exhibits and subjects from aeronautics to zoology.

Internet Encyclopedia of Philosophy
Search the site for a philosopher or browse the timeline of Western Philosophy. You can also find entries for specific beliefs, such as Confucianism and Rationalism.

To find more online encyclopedias, visit the following sites:

LibrarySpot Encyclopedias

Yahoo! Reference