Primary source

A record, object, or testimony created during the period or event being studied. Its status depends on the research question and how the evidence is used.

Secondary source: A work that analyzes, interprets, or synthesizes evidence from other sources. It contrasts with evidence created during the period under study.
Archival research: Research based on records preserved in archives and other repositories. Archives preserve letters, records, photographs, and other primary evidence.
Diary: A personal record of experiences and observations, usually written regularly over time. A contemporary diary can document an author's experiences and perceptions.
Digital preservation: The management of digital information to keep it accessible and usable over time. Born-digital primary sources can become unreadable without continued preservation.
Tertiary source: A work that compiles or summarizes information from primary and secondary sources. It is usually further removed from the events than a primary source.
Oral history: The collection and study of recorded personal accounts of past events and experiences. Recorded testimony can preserve firsthand memories of an event.
Photograph: An image made by recording light on a photosensitive surface or digital sensor. A photograph can preserve visual evidence from the time it depicts.
Memory: The mental capacity to encode, retain, and retrieve information and experience. Testimony recorded later depends on memory, which can change over time.
Historical method: A set of practices historians use to investigate the past through evidence and interpretation. It provides methods for evaluating primary-source evidence.
Legal evidence: Information or material presented to establish facts in a legal proceeding. Documents and objects may serve as original evidence in court.

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