The Idflieg designation system was used to classify German heavier-than-air military aircraft from the early days of the Fliegertruppe/Luftstreitkräfte to the end of World War I. The system evolved during this period as new classes of aircraft came into use.

The Deutsche Luftstreitkräfte —known before October 1916 as Die Fliegertruppen des deutschen Kaiserreiches —was the air arm of the Imperial German Army. In English-language sources it is usually referred to as the Imperial German Air Service, although that is not a literal translation of either name. German naval aviators of the Marine-Fliegerabteilung were an integral part of the Imperial German Navy. Both military branches operated aeroplanes, observation balloons and airships.