What are primary sources? Primary sources enable the researcher to get as close as possible to what actually happened during an historical event or time period. Primary sources can be treaties, photographs, legislation, diaries, speeches, interviews, letters, manuscripts, newspaper articles, artifacts, or other materials -- generally from the time of study (although, with oral histories, for example, they might be reflections of the past).
Primary sources can be in any format. Primary sources might be original documents in archives, republished in a contemporary book, available online, or preserved on microfilm. The content of the material -- rather than the format -- determines whether or not it's a primary source.
[Image: Illuminated manuscript pages. Nativity scene illumination II. Library of Congress, Prints and Photographs Division, Theodor Horydczak Collection. LC-H8-CT-C03-022-A DLC (color corrected film copy slide)]