An electrical engineer and senior editor for Aviation Week and Space Technology, Philip Klass began investigating UFOs in 1966 after participating in a panel discussion on the subject for the Institute of Electrical and Electronics Engineers (IEEE). From that time forward Klass has investigated UFO sightings in an effort to find a credible prosaic explanation, and became one of the most widely recognized UFO "debunkers." A founding member of the Committee for the Scientific Investigation of Claims of the Paranormal (CSICOP), serving on the Executive Council and the UFO subcommittee, Klass has authored seven books and numerous articles on UFOs, including the Skeptics UFO Newsletter in 1989. In the early 1970s, he became interested in space based weapons, and began collecting material related to the Strategic Defense Initiative (SDI) for a possible book. The Klass Collection relate to his forty-plus years of investigating UFO sightings, and includes correspondence with many of the leading UFOlogists, both pro and con. The collection contains case files, subject files, and correspondence. In addition, Klass' SDI material is included.

This rich collection of letters and documents, which was assembled by Sol Feinstone (1888-1980) over a period of fifty years, includes material on almost all notable Americans from before the Revolution to the 1850's, as well as prominent Europeans, and there are documents relating to military affairs. There are substantial groups of letters from: John Adams, Henry Dearborn, Alexander Hamilton, Jedediah Huntington, Thomas Jefferson, Lafayette, George Washington, and a long run of letters from a Massachusetts military surgeon named Samuel Adams. Many letters, though written by Revolutionary figures, relate to events that occurred before or after the War.