This document discusses key concepts for historians in evaluating primary and secondary sources. It defines primary sources as those created during the time period being studied, and secondary sources as those created afterwards. When determining usefulness, reliability, and limitations, historians consider factors like the author, date, intended audience, message, and completeness of information. While primary sources have the advantage of being contemporaneous, both primary and secondary sources can be useful or unreliable depending on thorough analysis. The reliability of a source may also depend on balancing multiple perspectives.