The Warren Commission is the popular name of the President's Commission on the Assassination of President Kennedy. The group was formed to investigate the events of November 22, 1963 in Dallas, Texas. The Warren Commission Report helped the Secret Service improve their protection of future presidents, but mostly the report has served as fodder for conspiracy theorists because of many omissions and conclusions contained within.
The Warren Commission Report is out of print, but is available online at the National Archives site. It's 888 pages long, but feel free to have at it. Additional material on the Kennedy assassination is available through links on the left-hand side of the page at the National Archives site or through the AARC Public Library.