单翼机泛指固定翼飞机当中，仅有单一机翼设计的机种，有别于两片或者是更多机翼的设计。虽然在1920年代以前，双翼或是多翼机是主流的设计，但是单翼机出现的时候并没有比较晚，仅是种类和数量较少。

到了1930年代，由于对飞行速度以及航程的要求，多片机翼产生的阻力与多余的重量，并不利于性能的提升。加上金属材质和悬臂（Cantilever）结构设计日趋成熟，单翼机逐渐取代多翼机，成为航空上的主流设计。到了1940年代中期，双翼机无论是在军用或者是民航机市场，都仅剩下占有非常少的数量。

A monoplane is a fixed-wing aircraft with a single main wing plane, in contrast to a biplane or other multiplane, each of which has multiple planes.

A monoplane has inherently the highest efficiency and lowest drag of any wing configuration and is the simplest to build. However during the early years of flight these advantages were offset by its greater weight and lower manoeuvrability, making it relatively rare until the 1930s. Since then the monoplane has been the most common form for a fixed-wing aircraft.