The materials historians use are often very fragmentary—a diary, a collection of posters, a set of deeds for a property. What turns these into credible evidence is the key skill of contextualizing many bits of information by weighing and comparing them. Are they typical of a larger setting or unique in themselves? Do they represent a particular moment or are they part of a longer pattern?

Historians are like detectives, trained to think about what kinds of sources might fill the gaps in what they know. They search through records and artifacts found in archives, libraries, and museums. They also explore physical landscapes and draw on the knowledge of individuals and communities with a stake in the histories they’re presenting. Interviews and other participatory research methods often make these kinds of evidence more collaborative and dynamic, especially for historians studying recent pasts and working with present-day communities.

Once historians have drafted their findings, whether in the form of books, exhibits, documentary films, reports, or other products, their evidence and interpretations are evaluated by other historians in various forms of “peer review,” meaning that they are usually scrutinized by others with specialized knowledge of the subject. This is one of the ways that historians’ interpretations of the past differ from those of most non-historians: they are created within a community of scholarship and practice based on certain shared standards of evidence and a careful consideration of previous study.

The Bracero History Archive, created through a partnership between the Smithsonian Institution’s National Museum of American History, the Roy Rosenzweig Center for History and New Media at George Mason University, the Center for the Study of Race and Ethnicity in America at Brown University, and the Institute of Oral History at the University of Texas at El Paso, traced the history of the 1942-1964 guest worker initiative that brought millions of Mexican agricultural workers into the US. The project drew on existing archival sources but also developed new digital collections through extensive community outreach and the recording of oral histories with former Bracero workers and their families.