Primary sources are the evidence of history, original records or objects created by participants or observers at the time historical events occurred or even well after events, as in memoirs and oral histories. Some primary sources, such as an autobiography or diary, are published but other sources, such as manuscripts, are not. Often, primary sources can be found using Google or Google Scholar.

Primary sources may include but are not limited to:

• Video recordings (Example: Genocide Archive of Rwanda)
• Correspondence, including letters and emails
• Data (Example: Cambodia Genocide Databases -  Yale University)
• Diaries, journals, and memoirs
• Documents produced by government or international agencies (Example: National Security Archive; UN Office on Genocide Prevention
• Manuscripts
• Maps (Example: Genocide Studies Program -Yale University;  Early Warning Project)
• Newspapers (Example: America's Historical Newspapers)
• Objects or artifacts (art objects, coins, clothing and fabric, weapons)
• Oral histories/Interviews/Memoirs/Testimonies (Example: Armenian Genocide Museum-Institute: Personal Histories)
• Photographs and Negatives (Example: Der Bildbestand der Deutschen Kolonialgesellschaft in der Universitätsbibliothek Frankfurt am Main )
• Speeches
• Trial and Court records (Example: Nuremberg Trials Project; Extraordinary Chambers in the Courts of Cambodia)

These sources serve as the raw materials historians use to interpret and analyze the past.

Secondary sources are works that reflect, interpret, critique or comment on earlier times. Secondary sources are one step removed from the event. Typical secondary sources include:

• Studies (books, journal articles, essays) that interpret, critique or summarize an event or time period
• Analysis or interpretation of data
• Biographies (not autobiographies)
• Bibliographies
• Dissertations (Example: Dissertations and Theses available through PQDT Open or ScholarsArchive@OSU)
• Documentaries
• Encyclopedias
• Gray literature
• Histories
• Reviews
• Textbooks

Secondary sources are often published in the form of books and journal articles. They may include portions of a primary source (such as a quote from a letter) or images and graphs.