The creation of an ileal reservoir ensures an improvement in the functional result obtained after ileo-anal anastomosis. As a result of its storage function, the reservoir allows a reduction in the number of stools per day. Several types of reservoir have been described. The S-shaped reservoir consists of three aniso-peristaltic limbs and an efferent loop with end-to-end ileo-anal anastomosis. The W reservoir is equivalent to a double J reservoir. The side-to-side iso-peristaltic reservoir consists of two iso-peristaltic limbs and an efferent loop with end-to-end ileo-anal anastomosis. After analysing the specific characteristics of each type of reservoir, the authors conclude that the necessity of a reservoir no longer needs to be demonstrated, but that there is no formal argument in favour of one particular model.