There are a number of different forms of chi sao, but they all share some common characteristics.

They are always two person exercises. The arms always start in contact at striking range They aim to the develop sensitivity to the opponents movements and energy, use of correct position, and ability to find a gap in an opponents defences, and the appropriate use of trapping skills.

The six stages of Chi Sau training are:

Dan Chi Sao (single sticking hands)
Poon Sao (double sticking hands)
Jeung Sao (changing hands)
Dok Sao (analytical hands)
Gor Sao (free applications)
Chi Sao Lye Bye Muk (blindfolded chi sao)
By looking at each of these stages in more detail we can gain a better understanding of the methods and aims of Chi Sao training.

Dan Chi Sao (single sticking hands)
Praticed in the Wing Chun training stance Using one hand the two practitioners alternate between striking and defending cycling through some of the basic hand techniques of the wing chun system. Practitioners try not to get into a predictable rythm and will both vary the speed of the drill randomly to ensure that they are maintaining an acute awareness of their partners movement.

Poon Sao (double sticking hands)
This is the second stage in Chi Sao training and is the only only stage where the movement is in a fixed and predictable sequence. Both arms are in contact as the two practitioners alternate between basic wing chun defensive positions ensuring that the centreline is defended at all times.

Jeung Sao (changing hands)
The practitioners learn to move from the outside to the inside of their opponents arms and back. Because they are particularly vulnerable to attack during these transitions they need to move quickly and maintain the optimal structure for their arm position.

Dok Sao (analytical hands)
Starting from poon sao the practitioners roll slowly seeking gaps in their partners defeence, as they find those gaps they push forward very slowly giving time for their partner to adjust to a better position. There are no set patterns and the exercise is an opportunity for practitioners to start experimenting with the basic positions and techniques that they've learned.

Gor Sao (free applications)
At full speed and starting from poon sau the practitioners aim to find gaps in their partners defences and deliver light taps to indicate where and how they could land a hit, and the same time they have to ensure that the same doesn't happen to themselves. Defence, trapping and striking skills can all be tested against a resisting opponent. It is essential that Chi Sao is done in a relaxed and non-aggressive manner for the student to get the optimum benefit in terms of training. Practitioners of wing chun talk about "playing" chi sau to emphasis the fact that it is to be done in a relaxed manner and frame of mind, that you would any game of skill.

Chi Sao Lye Bye Muk (blindfolded chi sau)
As you'd probably guess this builds on gor sau, adding the extra element of blindfolds to enhance the development of using contact to guage the position and defences of the other player.

Although chis sau unique to wing chun, similar principles are used in other systems, notably "Pushing Hands" in Tai Chi and "hubud-lobud" in Kali. Wing Chun Chi Sao has also been incorporated into Jeet Kune Do as one of the core training techniques.