The first 'jet fuels' were aviation gasoline (avgas), and the characteristics of subsequent jet fuels have evolved from this original choice, the available supply infrastructure, and the refiners' capabilities. Earlier on, it was evident that avgas would have to be altered to operate satisfactorily in jet-powered aircraft. The present contribution outlines the various requirements that led to the development of various operational jet fuels, including United States (US) Jet A (European Jet A-1), Jet Propellant JP-4 (European F-40), JP-5 (European F-44), JP-7 (US only), JP-8 (F-34), JP-TS (US only), and JP-8 + 100 (US only). The composition of aviation fuels has generally been determined by specifications that are primarily based upon operational requirements. These include heat content, fluidity, corrosion protection and stability. Moreover, cost is often a primary driver. The chemical composition variations of prototype aviation fuels are compared. Chemical and physical characteristics of the Fuels are reviewed within the context of operational requirements. The development of each product is put into the context of two very distinct models, which highlight the importance of cost considerations. A final aim is to foreshadow what may be to come, in the context of JP-8 + 225, JP-900, 'controlled chemically reacting fuels', and alternative fuel sources. Published by Elsevier Science Ltd.