Category:Project Blue Book

This category contains all officially recorded cases from the United States Air Force's Project Blue Book (1947–1969), the systematic investigation of unidentified flying objects (UFOs). The cases listed here are those officially classified as "Unknown" — sightings for which no conventional explanation was determined after investigation.

Project Blue Book investigated a total of 12,618 reported sightings. Of these, 701 were officially listed as "Unknowns" upon the project's termination on December 17, 1969. The records are held by the National Archives and Records Administration (NARA) as microfilm publication T-1206.

• Project Sign
• Project Grudge
• Condon Report
• J. Allen Hynek
• Edward J. Ruppelt

• National Archives – Project Blue Book Records
• NICAP – Complete List of Project Blue Book Unknowns