Side stroke is a swimming stroke, so named because the swimmer lies on one side.

This stroke allows the swimmer great endurance. Instead of working both arms and legs simultaneously in the same way, the side stroke uses them simultaneously but differently. A swimmer tired of exercising one side can just turn over and use the other, the change of action helping the limbs recover.

To begin, the swimmer may lie on the right side, stretching the right arm out as far as possible away from the feet, keeping the fingers of the right hand quite straight and the hand itself held edgewise, so as to cut the water like a shark's fin. The left hand is placed across the chest, its back against the right breast.

The legs make a scissor kick, in which the lower leg does the greater share of the work. Before its impetus is quite expended, the right arm comes round in a broad sweep, until the palm of the right hand almost touches the right thigh. At the same moment, the left hand makes a similar sweep, but is carried backwards as far as it can go.

This completes one cycle of the stroke, which is then repeated.

The hands act directly upon the water like oars, and do not waste any power by oblique action. In ordinary swimming on the right side the left arm moves gently in the water, almost at rest. Then, after some time, the swimmer turns on the other side, and the left arm has its chance to work while the right idles.

A modification of swimming on the side, is the trudgeon stroke.