M–SURGE: new software specifically designed for multistate capture–recapture models. M-SURGE (along with its companion program U-CARE) has been written specifically to handle multistate capture-recapture models and to alleviate their inherent difficulties (model specification, quality of convergence, flexibility of parameterization, assessment of fit). In its domain, M-SURGE covers a broader range of models than a general program like MARK (White & Burnham, 1999), while being more user-friendly than MS-SURVIV (Hines, 1994). Among the main features of M-SURGE is a wide class of models and a variety of parameterizations: (1) M-SURGE covers conditional models with probability of recapture depending on the current state (Arnason¿Schwarz type models) as well as on the current and previous state (Jolly-movement type models). In both cases, age and/or time-dependence and multiple groups can be considered. (2) Combined survival-transition probabilities can be represented as such or decomposed into transition and survival probabilities. (3) Among the transition probabilities with the same state of departure, the one to be computed by subtraction can be freely picked by the user. User-friendliness is enhanced by the easiness with which constrained models are built, using an interpreted language called GEMACO. Examples of various types of multistate models are developed and presented.