American Jurisprudence 2d (Am. Jur. 2d) and Corpus Juris Secundum (C.J.S.) are two good sources to consult to get basic information on an area of law.
Am. Jur. 2d is an encyclopedia containing over 400 separate titles on a broad range of legal topics. In Am. Jur. 2d, look in the Evidence and Expert and Opinion Evidence sections for information on evidence.
C.J.S. is a legal encyclopedia covering state and federal legal topics, and has been cited over 90,000 times by all levels of U.S. Courts.
The Congressional Research Service (CRS) serves the Congress throughout the legislative process by providing comprehensive and reliable legislative research and analysis that are timely, objective, authoritative, and confidential, thereby contributing to an informed national legislature.