The paper presents Visiplan, a knowledge-based modelling language that is applied to resource allocation and sequencing problems. Expert knowledge is encapsulated throughout the whole modelling and problem solving process. This enables the user’s effort to be targetted at defining what he or she wishes to solve (i.e. the problem) but not how to solve it (i.e. not the implementation details behind the optimisation technique). Approximation methods that mix artificial intelligence and operation research techniques are successfully used for solving combinatorial problems. The key elements of this approach are combined in a tool appropriate for solving resource allocation and sequencing problems.