A programme for electromagnetic computations has been developed at FOI. This programme is called FOIMoM and is based on the method of moments. It solves the electric field integral equation for perfect electric conductors in vacuum. There are already similar programmes available at FOI, for example FEKO which is a commercial programme, but the source code is not available. FOIMoM has been developed for a number of reasons: in order to increase the competence, in order to gain control of different algorithms, and in order to be able to introduce new functionality at a later stage.