The Learjet Model 35 and Model 36 are a series of American multi-role business jets and military transport aircraft manufactured by Learjet between 1973 and 1993. When used by the United States Air Force, they carry the designation C-21A. Learjet was acquired by Bombardier Aviation in 1990 and is now a subsidiary, so the aircraft is also known as the Bombardier Learjet 35.

Learjet was a manufacturer of business jets for civilian and military use based in Wichita, Kansas, United States. Founded in the late 1950s by William Powell Lear as Swiss American Aviation Corporation, it became a subsidiary of Canadian Bombardier Aerospace in 1990, which marketed the company’s aircraft as the "Bombardier Learjet Family". The 3,000th Learjet was delivered in June 2017. The Learjet line was once sufficiently popular that the Learjet name became synonymous and interchangeable with the terms business jet or private jet in the popular vernacular. In February 2021, Bombardier announced the end of production for all new Learjet aircraft in 2021, with the continuation of support and maintenance for aircraft currently in service.