Abstract: A surfing sail includes a basic sail, whose luff is attached to a mast associated in the usual way with a boom to the aft end of which is attached the clew of the basic sail and an auxiliary sail which serves reefing purposes. The auxiliary sail is triangular, narrow and long and its headboard is attached pivotally to the basic sail adjacent its top and in the proximity of the leech. At its foot region and at a level corresponding to the boom, the auxiliary sail is fitted with a guide batten, which is curved and arranged such that during pivotal movement of the auxiliary sail it is displaced along a circular path. The radius of the circular path corresponds to the distance of the guide batten from the pivot on which the auxiliary sail is fixed to the basic sail. The guide batten is guided longitudinally. The auxiliary sail can be reefed or taken out during surfing in a simple and easy manner, such that a windsurfer can reef or take out the surfing sail during surfing without any attendant problems.