A half-pipe is a structure used in gravity extreme sports such as snowboarding, skateboarding, skiing, freestyle BMX and inline skating. The structure is usually wood, although sometimes the surface is made of another material such as concrete, metal, dirt or snow. In appearance, it resembles a cross section of a swimming-pool, and in its most basic form, it consists of two concave ramps (or quarterpipes), topped by copings and decks, facing each other across a transition. Originally half-pipes were simply half sections of a large pipe. Since the 1980s, half-pipes have had extended flat ground (the flat bottom) between the quarterpipes and the original style half-pipes have become deprecated. The flat ground gives the athlete time to regain balance after landing and more time to prepare for the next trick.

The attraction of the half-pipe lies in the fact that a skilled athlete can perform on it for an extended period of time, using a technique called pumping, to attain extreme speeds, while expending relatively little effort. Large (high amplitude) half-pipes make possible many of the aerial tricks in BMX, in-line skating and skateboarding.

For winter sports such as freestyle skiing or snowboarding, a half-pipe can be dug out of the ground or created by piling snow up. The plane of the transition is oriented downhill at a slight grade to allow riders to use gravity to develop speed and facilitate drainage of melt. In the absence of snow, dug out half-pipes can be used by dirtboarders, motorcyclists, and mountain bikers.

Performance in a half pipe has been rapidly increasing over recent years. The current limit performed by a top level athlete for a rotational trick in a halfpipe is 1440 degrees (4 full 360 degree rotations). In top level competitions rotation is generally limited to improve 'style and flow'.