Primary sources are materials that provide first-hand documentation or knowledge, usually of people, places, events or time periods. Primary sources enable the researcher to trace a research subject to its origin, potentially supporting new interpretations or revealing previously undocumented knowledge of that subject. Just a few examples of primary sources include diaries, oral histories, fossils, DNA, correspondence, speeches, interviews, court cases, or scientific studies. Secondary sources build upon or extrapolate information derived from primary sources, and the distinction between the two can be quite fluid depending on one's area of study. In most contexts, however, a primary source is understood to be a point of origin, or a piece of raw data, for a research subject.
Going to the Sources: A Guide to Historical Research and Writing (Online access)