B-Conditions identity markings have been applied to British aircraft used for experimental purposes and flight testing since their introduction in 1929. They are neither a civil registration nor a military serial number. They provide an identity to aircraft which do not yet have a Certificate of Airworthiness and are used prior to being placed on the civil or military aircraft register. There is no official B-Conditions register. With the temporary nature of these markings, details of their usage can only be discovered from personal observation and the work of aviation historians. This book is the result of many years of painstaking research and contains listings of all known B-Conditions allocations up to the present day. As well as well-known types, the book features such lesser known aircraft as the Handley Page Manx tailless aircraft, the Short S.31 half size aerodynamic test bed for the Short Stirling, the Supermarine Speed Spitfire, the Miles M.35 Libellula tandem wing naval fighter test bed, the Saunders Roe SR.A/1 flying boat fighter, Lancasters used by Flight Refuelling Ltd for in-flight refuelling tests, and Napier’s crop-spraying Bensen gyrocopters. There are also extensive lists of production aircraft and refurbished aircraft for onward sale. However, it is much more than just a listing of individual aircraft. The history of the British aircraft industry, and its proud record of aviation experimentation and development is to be found in the separate entries covering the UK’s aircraft manufacturers. Many once familiar names have passed into history through amalgamation or bankruptcy.