. . . are original records created at the time an historical event occurred; they may also be written well after-the-fact by participants in the event. (Think of memoirs, autobiographies, or transcriptions of recollections - i.e. oral histories.)
. . .need not focus on a specific event; rather, they may more generally reflect the ideas and values of a particular time period. Examples of these include etiquette books, marriage manuals, books on manhood, physical fitness, race, religion, education, etc.
. . . may include personal writings such as letters, diaries, journals, memoirs, and autobiographies (in manuscript or published form). They may also include newspaper articles or editorials, speeches, interviews.
. . . may be produced by governments and organizations, for example, Congress, the Office of the President, the American Eugenics Society, and the Domestic and Foreign Missionary Society.
. . . need not be "non-fiction" works - or written works. They may be creative works, such as poems, novels, and plays, as well as photographs, audio recordings, moving pictures, sheet music, etc.
In short, primary sources serve as the raw material to interpret the past, and when they are used along with previous interpretations by historians, they provide the resources necessary for historical research.
Adapted from Using Primary Sources on the Web, History Section, Reference and User Services Association, American Library Association, accessed 3/26/12]
For an overview of primary sources available at Smith and in the Five Colleges, consult the Find Primary Sources page.