As investigators of the past, historians rely on both primary sources and secondary sources. Primary sources are materials from the historical period being studied—government documents, numerical data, speeches, diaries, letters, and maps. Secondary sources are materials produced after the historical period that interpret or synthesize historical events. The same source can function as either a primary or a secondary source depending on what you are writing about. For example, a newspaper article about Slobodan Milosevic’s decision to defend himself during his war crimes trial would be a secondary source in an essay about why Milosevic made this decision. The same article, however, would be a primary source in an essay about newspaper coverage of Milosevic’s war crimes trial.
Following are some of the ways historians use evidence.