A useful, and constantly developing resource is Wikipedia, the free encyclopedia. This is multi-authored and therefore to be used with caution, but does give helpful, if brief, introductory summaries on a surprisingly wide range of topics (with versions in languages other than English). The current version of the Encyclopedia Britannica was originally released onto the web without charge but its useful articles are now available only on subscription. However, 'over 57,000 articles' from the 6th Edition of the Columbia Encyclopedia can be accessed free of charge via HighBeam.

For historical encyclopedias the following are online:

• Ephraim Chambers, Cyclopaedia, or, An universal dictionary of arts and sciences (1728) (University of Wisconsin Digital Collections)
• 1911 Enclopaedia Britannica (see the Wikipedia entry for free online versions)

For biographical information see the People links.