Often, an important step in evaluating any source you intend to use in your research is to determine whether it is a primary, secondary, or tertiary source. You may be given an assignment that requires you to use a particular kind of source; it is thus necessary to know how to identify them. This page defines primary, secondary, and tertiary sources and provides examples of each.
NOTE: Whether a particular source should be considered primary, secondary, or tertiary depends on your research focus. For example, Denis Diderot's Encyclopédie, published in eighteenth-century France, was an encyclopedia, which would generally be categorized as a tertiary source. Scholars today, however, use the Encyclopédie as a primary source to study the ideas and views of Enlightenment thinkers.