PRIMARY SOURCE: Something that was written or produced in the time period you are investigating (letters, speeches, diaries, newspaper articles from the time, oral history interviews of people from the time, documents, photographs, artifacts, and anything else that provides firsthand 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. An article about the Vietnam War published in 2001 and not written by an eyewitness or participant about his or her experience is not a primary source. An interview with an expert (such as a professor of Vietnamese history) is not a primary source UNLESS that expert actually lived through and has firsthand knowledge of the events being described. Primary materials such as quotes from historical figures or photographs of historical events, when found in secondary sources, can be used effectively in NHD projects; however, these are not considered primary sources.