IRIS (Interactive Robustness analysis and parameters’ Inference for multicriteria Sorting) is a Decision Support Software designed to address the problem of sorting a set of actions (alternatives, projects, candidates, etc.) into predefined ordered categories, according to their evaluations (performances) on multiple criteria. For instance, it may be used to sort funding requests according to merit categories (e.g. “Very good”, “Good”, “Fair”, “Not eligible”), or to sort loan applicants into categories (e.g. “Accept”, “Require more collateral”, “Reject”), or to sort employees in a company into categories that define incentive packages, etc. IRIS implements the methodology presented in Dias et al. (2002), using a pessimistic concordance-only variant of the ELECTRE TRI method. Rather than demanding precise values for the ELECTRE TRI parameters, IRIS allows to enter constraints on these values, namely assignment examples that it tries to restore. It adds a module to identify the source of inconsistency among the constraints when it is not possible to respect all of them at the same time, according to a method described in Mousseau et al. (2002). On the other hand, if the constraints are compatible with multiple assignments for the actions, IRIS allows drawing robust conclusions by indicating the range of assignments (for each action) that do not contradict any constraint.