The most basic definition of a primary source is that which is written or produced in the time period students are investigating. Primary sources are materials directly related to a topic by time or participation. These materials include letters, speeches, diaries, newspaper articles from the time, oral history interview, documents, photographs, artifacts, or anything else that provides first-hand accounts about a person or event. This definition also applies to primary sources found on the Internet. A letter written by President Lincoln in 1862 is a primary source for a student researching the Civil War era. A newspaper article about the Battle of Gettysburg written by a contemporary in July 1863 would be a primary source, but an article about the battle written in June 2001 could not have been written by an eyewitness or participant and would not be a primary source. The memories of a person who took part in the battle also can serve as a primary source, as he or she was an eyewitness to and a participant in this historical event. However, an interview with an expert — a professor of Civil War history, for example — is not a primary source UNLESS that expert actually lived through the events and has firsthand knowledge of them (unlikely for a Civil War historian writing today).
Note: Primary materials such as quotes from historical figures and photographs of historical events can be found in secondary sources and used effectively in history fair projects. However, these are not considered primary sources until the researcher has interacted with the original source of the quote or photograph.
Secondary sources are usually published books or articles by authors who were not eyewitnesses to or participants in the historical event or period. These writers base their interpretation on primary sources, research, and study. Secondary sources provide context for a historical event. For example, history textbooks and other history books about a particular topic are secondary sources. Other secondary sources include biographies, newspaper retrospectives, and reference books such as encyclopedias. This definition also applies to secondary sources found on the Internet, such as study and curriculum guides, blogs, and Wikipedia.