The Boeing 737 is a short- to medium-range, twin-engine

Twinjet

A twinjet or twin jet is a jet aircraft powered by two engines. Such configuration of an aircraft is the most popular today for commercial airliners, for fighters, and many other kinds, because while offering safety from a single engine failure, it is also acceptably fuel-efficient.-Aircraft...

 narrow-body

Narrow-body aircraft

A narrow-body aircraft is an airliner with a fuselage aircraft cabin width typically of 3 to 4 metres , and airline seat arranged 2 to 6 abreast along a single aisle...

 jet airliner

Jet airliner

A jet airliner is an airliner that is powered by jet engines. This term is sometimes contracted to jetliner or jet.In contrast to today's relatively fuel-efficient, turbofan-powered air travel, first generation jet airliner travel was noisy and fuel inefficient...

. Originally developed as a shorter, lower-cost twin-engine airliner derived from Boeing's 707

Boeing 707

The Boeing 707 is a four-engine narrow-body commercial passenger jet airliner developed by Boeing in the early 1950s. Its name is most commonly pronounced as "Seven Oh Seven". The first airline to operate the 707 was Pan American World Airways, inaugurating the type's first commercial flight on...

 and 727

Boeing 727

The Boeing 727 is a mid-size, narrow-body, three-engine, T-tailed commercial jet airliner, manufactured by Boeing. The Boeing 727 first flew in 1963, and for over a decade more were built per year than any other jet airliner. When production ended in 1984 a total of 1,832 aircraft had been produced...

, the 737 has developed into a family of nine passenger models with a capacity of 85 to 215 passengers. The 737 is Boeing's only narrow-body airliner in production, with the -600, -700, -800, and -900ER variants currently being built.

Originally envisioned in 1964, the initial 737-100 first flew in 1967, and entered airline service in February 1968.