The Boeing 737 is a short- to medium-range twinjet narrow-body airliner. Originally developed as a shorter, lower-cost twin-engined airliner derived from Boeing's 707 and 727, the 737 has developed into a family of ten passenger models with a capacity of 85 to 215 passengers. The 737 is Boeing's only narrow-body airliner in production, with the -700, -800, and -900ER variants currently being built.