Project Blue Book (1952–January 17, 1969) was the third and longest-running US Air Force program to officially investigate UFOs, following Project Sign (1948) and Project Grudge (1949). Headquartered at Wright-Patterson AFB, Ohio. SCALE: 12,618 UFO reports catalogued. Of these: ~90% eventually classified as “identified” (astronomical objects, aircraft, hoaxes, atmospheric phenomena). ~6% (701 cases) remained “Unidentified” — insufficient information to assign a conventional explanation. J. ALLEN HYNEK: Astronomer at Ohio State University, served as Blue Book’s scientific consultant from 1948 until closure. Initially hired to debunk UFO reports. Over 20 years, Hynek’s skepticism eroded as he encountered cases that resisted conventional explanation. He developed the Close Encounter classification system (CE1-CE3 = sighting, physical evidence, beings observed) still used today. Founded the Center for UFO Studies (CUFOS) after Blue Book closed. Hynek’s transformation from official skeptic to credentialed advocate is the definitive model for how serious investigation changes conclusions. THE CONDON REPORT (1969): University of Colorado study led by physicist Edward Condon, funded by the Air Force. Concluded Blue Book was not “scientifically useful” and that studying UFOs would not benefit science. Blue Book was officially terminated January 17, 1969. SIGNIFICANCE: Blue Book’s closure created a 50-year gap in official US government UAP research. No classified program was publicly acknowledged until AATIP/AAWSAP (2007-2012) and UAPTF (2019). The 701 unexplained Blue Book cases remain in the NARA record group; UAP researchers continue to analyze them. Blue Book’s conclusion that UFOs posed “no national security threat” has been directly contradicted by every subsequent disclosure program.