Primary sources are the raw materials of history — original documents and objects which were created at the time under study. They are different from secondary sources, accounts or interpretations of events created by someone without firsthand experience. A letter written by Beethoven describing his compositional process as opposed to a student giving an account of how Beethoven composed. A Mozart manuscript in his own hand as opposed to an engraver's plate from a music publisher taken from a score edited by Costanza or a student.