Encyclopedia Smithsonian
- Links to on-line Smithsonian resources and answers to frequently asked questions from A to Z.
- http://www.si.edu/Encyclopedia_SI/start.htm

Information Please
- On-Line dictionary, Internet encyclopedia, and almanac reference.
- http://www.infoplease.com/

Simple English Wikipedia
- User-contributed online encyclopedia intended for people whose first language is not English.
- http://simple.wikipedia.org/

Wikipedia
- A free encyclopedia built collaboratively using Wiki software. (GNU Free Documentation License) and with over 1,000,000 articles. Note that because articles can be "vandalized," information on Wikipedia is not always accurate.
- http://en.wikipedia.org/wiki/Main_Page

Hutchinson Encyclopedia
- "A subset of the content (concise set) is provided for free, the access to the rest of the Hutchinson Encyclopedia requires subscription."
- http://encyclopedia.farlex.com/

MSN Encarta Encyclopedia
- Online home of the Encarta encyclopedia, world atlas, dictionary, thesaurus, multimedia collection, and homework tools.
- http://encarta.msn.com/

Bartleby.com
- Includes the Columbia Encyclopedia, Sixth Edition, dictionaries, thesauri, and more.
- http://www.bartleby.com/

Britannica Concise
- Featuring 28,000 short articles.
- http://concise.britannica.com/

Nuttall Encyclopædia of General Knowledge
- Approximately 14,000 entries on topics including art, geography, literature, philosophy, religion. Originally published in 1907.
- http://www.fromoldbooks.org/Wood-NuttallEncyclopaedia/

Encyclopaedia Britannica Online
- Provides complete text of Encyclopaedia Britannica with search capabilities, related links, and multimedia enhancements. Full text for subscribers only; free trial available.
- http://www.britannica.com/

1911 Encyclopedia Britannica
- Offers the 11th Edition Encyclopedia Britannica which is now in the public domain. All articles are searchable and alphabetized.
- http://encyclopedia.jrank.org/

Wikinfo
- User edited encyclopedia based on Wiki software. Contains articles, information on editing, and a list of differences between this encyclopedia and Wikipedia.
- http://www.wikinfo.org/

How Stuff Works
- Articles explain how hundreds of things work, from elements of the human body to space-age technology.
- http://www.howstuffworks.com/

The LoveToKnow Free Online Encyclopedia
- Browsable. Based on the eleventh edition of the Encyclopedia Britannica, first published in 1911.
- http://www.1911encyclopedia.org/

Encyberpedia
- Electronic encyclopedia with its own content as well as over 10,000 links to the best reference sites on the Internet.
- http://www.encyberpedia.com/cyberlinks/links/index.html

The Probert Encyclopaedia
- Reference source with several hypertext linked entries covering a broad variety of subjects.
- http://www.probert-encyclopaedia.co.uk/

World Book Encyclopedia
- Online version of the complete reference work along with dictionary, atlas, links, magazines, historical documents, audio, video, images, and 3D photographs. Requires free temporary registration with option to buy continued access for full articles.
- http://www.worldbook.com/