Primary sources are first-hand accounts of events and experiences, both public and personal. These accounts are recorded in a variety of formats, both published and unpublished. Newspapers are examples of published primary sources. Letters, diaries, photographs, and field recordings are examples of unpublished primary sources. These "remains of the day" - what has survived and been preserved - illuminate a past we would not otherwise know. They allow researchers to eavesdrop on the past and in a sense to travel back in time by telling the stories of a past witnessed or experienced by the records' creators. Historians use primary sources to reconstruct and interpret the past, and thus primary sources are the "raw materials" of history.

Primary sources originate from different points in time. Some sources such as letters from the battlefront, photographs, and daily diaries are created close to the time of the experience. Others are recorded years later in the form of oral and written recollections.