Biographical essays on anyone who died before 1996 and "whose significant actions occurred during his or her residence within what is now the United States or whose life or career directly influenced the course of American history."

"Significance" includes achievement (superior accomplishment as judged by contemporaries), fame (celebrity or notoriety), or influence (effect on one's own time despite lack of public notice). Even some "ordinary" persons have been included if they left autobiographies, diaries, or other artifacts that attracted posthumous attention.

Content (from http://www.anb.org/onlinefeatures.html):

• New biographies added quarterly in January, April, July and October -- including articles on recently deceased notables as well as figures from the past who were not subjects in the print edition.
• Nearly 2,500 illustrations with more added with each quarterly update or more frequently
• Regular updates to the bibliographies
• Regular updates to the biographies that incorporate new facts and new interpretations

"Subjects included in the original print edition of the ANB had to have died before the end of 1995; the ANB Online will include future entries on important figures who have died since then. It will also fill in the historical record by adding biographies of influential figures who were not included in the print edition."