Types of Source Materials There are two major types of source material used by researchers; these are known as primary and secondary sources. Primary sources provide firsthand accounts about a person or event. They include letters, diaries, speeches, interviews, newspaper articles from the time, and many other types of documents. Secondary sources are usually published books or articles in which the author presents a personal interpretation of a topic, based on primary sources. Most library books are secondary sources, as are encyclopedias. Secondary sources are important because they show how people have formed different opinions about historical events. Primary Source Material Secondary Source Material Using the Internet