The Boeing 737 is a short- to medium-range, twin-engine narrow-body jet airliner. Originally developed as a shorter, lower-cost twin-engine airliner derived from Boeing's 707 and 727, the 737 has developed into a family of nine passenger models with a capacity of 85 to 215 passengers. The 737 Next Generation comprises the four currently built -600, -700, -800, and -900ER models, ranging from 102 ft (31.09 m) to 138 ft (42.06 m) in length.