Recommended Reading
(a deliberately short list)

The UFO Enigma: A New Review of the Physical Evidence
Peter Sturrock
(Stanford University physics professor)

The UFO Evidence – Volume 2 : A Thirty Year Report
Richard Hall

CE-5: Close Encounters of the Fifth Kind
Richard F. Haines
(retired NASA psychologist)
WARNING: The cover of this book shows the standard model gray alien (that’s a particle physics — also cosmology — joke). Remember the old maxim though: Don’t judge a book by its cover. But you might want to have this one shipped to your home instead of your office.

UFOs and the National Security State: An Unclassified History. Vol. 1: 1947-1973
Richard Dolan

The Missing Times
Terry Hansen
(well documented history of ties between the national media and the intelligence community)

UFOs and Abductions: Challenging the Borders of Knowledge
David Jacobs, editor
(A Univ. of Kansas Press anthology)

The UFO Experience: A Scientific Inquiry
J. Allen Hynek
(Reprint of a classic book by the late Northwestern Univ. astronomy professor and Air Force consultant)

Unconventional Flying Objects: A Scientific Analysis
Paul R. Hill
(retired NASA engineer)

Journal of UFO Studies (JUFOS)
(published by the Hynek Center for UFO Studies)