Strain wave gear is a special type of mechanical gear system that can improve certain characteristics compared to traditional gearing systems. It is very commonly implemented in robotics, for gear reduction but may also be used to increase rotational speed, or for differential gearing.

The strain wave gear is mainly composed of four basic components: a wave generator, flexible gear, flexible bearing and rigid gear. It is a gear transmission in which a flexible bearing is assembled by a wave generator to make a controllable elastic deformation of the flexible gear and mesh with the rigid gear to transmit motion and power.

So, high gear reduction ratios are possible in a small volume (a ratio from 30:1 up to 320:1 is possible in the same space in which planetary gears typically only produce a 10:1 ratio).