The Learjet Model 35 and Model 36 are a series of American multi-role business jets and military transport aircraft. When used by the United States Air Force they carry the designation C-21A.

The aircraft are powered by two Garrett TFE731-2 turbofan engines. Its cabin can be arranged for 6-8 passengers. The Model 36 has a shortened passenger area in the fuselage, in order to provide more space in the aft fuselage for fuel tanks. It is designed for longer-range mission capability.

The engines are mounted in nacelles on the sides of the aft fuselage. The wings are equipped with single-slotted flaps. The wingtip fuel tanks distinguish the design from other aircraft having similar functions.

The Model 36 is essentially identical to the 35, except that it has a larger fuselage fuel tank, giving it 500 miles longer range, but reducing the passenger area’s length by 18 inches (0.46 m). It was certified, along with the 35, in July, 1974.