Waterbending is one of the four elemental bending arts, the hydrokinetic ability to control water, as well as its many forms. The people of the Water Tribe utilize this type of bending. In turn, the Water Tribes are divided up in to the Southern Water Tribe, the Northern Water Tribe, and the lesser known Foggy Swamp Tribe.
Water is the element of change. The moon is the source of power in waterbending, and the original waterbenders learned from the moon by observing how the moon pushed and pulled the tides. The Water Tribes are the only people to not learn bending from an animal. The fighting style of waterbending is mostly flowing and graceful; acting in concert with their environment. However, Foggy Swamp Style waterbending is more rigid and straight - probably in concert with the often stagnant nature of the water in their swamp. Waterbenders deal with the flow of energy; they let their defense become their offense, turning their opponents' own forces against them.
Waterbending is based on a style of T'ai chi ch'uan (specifically the Yang style). It is a Chinese martial art that features slow movements and elegant forms that evoke the feel of flowing water. Waterbending provides a versatility of experience. Waterbending's strength is its defensive capabilities which, rather than supporting a separate set of offensive methods, are transformed into attacks and counters - defense into offense. Rather than simply stopping to deflect an attack, waterbending's defensive maneuvers focus on control, achieved through turning an opponent's own strength against him, instead of directly harming the opponent. According to Iroh, water is the element of change.
The closest thing to becoming an waterbender in the real world is to become a master in T'ai chi ch'uan.