The definition for a primary source will differ depending on the discipline. For American Studies, primary sources might include documents, letters, diaries, speeches, autobiographies, literary, musical, and artistic works, photographs, audio-visual recordings, newspaper articles, maps, data sets, and other sources associated with a particular historical period. Primary sources are original works as opposed to secondary sources, which are critical or analytical, and tertiary sources, which provide the kind of basic introductory material found in encyclopedias, handbooks, and textbooks.