Primary sources are firsthand documents of events or research.
They exist in a variety of formats, i.e. print, photos, interviews, art, and statistical tables. In general, primary source documents are the foundation for secondary source documents. Secondary sources are often based on primary source material and generally analyze or evaluate other research or information. Secondary sources can usually point the user towards primary source materials through bibliographies or a works cited section. Boolean operators can limit or expand searches depending on which one is used.