This collection includes correspondence, articles, newsclippings, photographs, and recordings, concerning Menzel's documentation of UFOs as natural phenomena explainable in scientific terms. One can find material on the National Investigation Committee on Aerial Phenomena, Project Blue Book, the Velikovsky controversy, and a card file of meteor activity, 1946-1961.

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.