The first provisional jet fuel specifications were published in 1943 in England (RDE/F/KER/210) and 1944 in the U.S. (AN-F-32a). Jet fuel has undergone many changes in subsequent years, with current specifications for JP-5 and JP-8 for the military in the U.S. and Jet A/Jet A-1 for commercial use worldwide. Jet fuel specifications are subject to constant tension between performance requirements and availability/cost considerations. In this paper we will discuss how jet fuels have evolved over the years from the first engines to current gas turbine engines. Jet fuels derived from nonpetroleum sources will also be discussed.