Primary sources are documents that were created either during the historical period being studied, or after that period by someone who participated in the events. They reflect the experience of a participant or observer and are valuable for providing a first-hand perspective on events that may have happened far in the past. (However, not everyone agrees on what constitutes a primary or secondary source in any given situation. Check with your professor to be sure!)
Primary sources can be in almost any format. Books, periodicals, photographs, artworks, letters, diaries, government documents, business records, maps, audio and video recordings, speeches, films, and digital files may all be considered primary sources if they fit the definition above.
Primary sources can be found in a variety of locations. Some are in printed books in the library. Some might be in microfilm or microfiche collections. Some may be available online, either in a database we pay for, or on the free Internet. Original documents and other artifacts may be in Special Collections and Archives.
What you already know about your topic will help determine your search strategies for primary sources. Make sure you have a grasp of important people, organizations or agencies, places, and dates relating to your research, at least in broad terms, before you begin your search for primary sources. You can search more efficiently with this information already in hand. Reference sources and secondary sources are good places to look for background information.
A helpful video from the Minnesota Historical Society.
Remember, not everyone agrees on what constitutes a primary or secondary source in any given situation. Check with your professor to be sure!