The 90th Aero Squadron was an Air Service, United States Army unit that fought on the Western Front during World War I. The squadron was assigned as a Corps Observation Squadron, performing short-range, tactical reconnaissance over the III Corps, United States First Army sector of the Western Front in France, providing battlefield intelligence. After the 1918 Armistice with Germany, the squadron returned to the United States in May 1919 and became part of the permanent United States Army Air Service in 1921, being re-designated as the 90th Squadron (Surveillance).