A Jagdstaffel (plural Jadgdstaffeln; often abbreviated to Jasta) was a fighter Staffel (squadron) of the German Imperial Luftstreitkräfte during World War I.
Before April 1916, the German Army's Military Aviation Service, (Die Fliegertruppen des deutschen Kaiserreiches) which had existed since 1912, was largely organised in small general purpose units (Feldfliegerabteilung) - although the formation of the first specialised bombing and close support units had begun during 1915. The Feldfliegerabteilung were completely subservient to the Army command to which they were attached.
In the aftermath of the Battle of Verdun - during which the German side lost the air superiority built up during the so-called Fokker Scourge, and in particular, as a result of the superior performance of the Royal Flying Corps during the Battle of the Somme, a complete reorganisation of the German flying service took place. It was greatly expanded, renamed the Deutschen Luftstreitkräfte (reflecting a far greater degree of autonomy, although it remained an integral part of the army), and acquired a far greater number and variety of specialist units, including the first single-seater fighter units in German service, the Jagdstaffeln (literally, "hunting squadrons").
By the end of the spring of 1915 the first German fighter aircraft were being issued in small numbers to various ordinary Feldflieger-Abteilungen. At this period their function was seen almost entirely as "protection" for the reconnaissance missions which were the primary responsibility of the German air service. Such pioneering pilots as Kurt Wintgens, Max Immelmann and Oswald Boelcke pioneered the more aggressive use of the early Fokker Eindecker fighters, but it was to be almost a year before the first specialist fighter units joined the Fliegertruppe.