The Schweizer SGS 1-21 is a United States single-seat, mid-wing, Open Class glider built by Schweizer Aircraft of Elmira, New York.

The 1-21 was a clean-sheet design intended to fill the role of high performance competition sailplane. It was designed by Ernest Schweizer and first announced in the September-October 1946 issue of the Soaring Society of America's Soaring magazine.

Following World War II soaring in the United States was dominated by surplus two-place gliders that had been used as trainers by the military, such as the TG-1, TG-2 and TG-3.

By the end of the war there were only about 400 gliders in the US. Of these only about a dozen were high performance competition sailplanes and half of these were pre-war designs. Schweizer Aircraft realized that if the US was to progress in the sport of soaring, that domestic mass-produced, high performance sailplanes would be needed.

The 1-21 was designed to be the high performance sailplane of choice in the post war era. While design had been completed in the summer of 1946, Schweizer had not built a prototype, hoping to get sufficient orders to make it worthwhile.