The model we present in this report is mainly developed on work done together with the company Gatsoft AS. With minor changes and extensions, a version of the model has been implemented and delivered to Gatsoft as a plug-in to the rostering part of their software GAT. The model consists of two types of constraints; hard and soft. The hard constraints must never be violated. The origin of the hard constraint is typically legislation or working acts. The soft constraints can be violated, but we try to avoid it. Violating the soft constraints is usually necessary to be able to find a solution. A solution to the model is one in which all hard constraints are satisfied. The quality (objective function value) of the solution is measured in terms of violations to the soft constraints.