Requirements represent essential input for software projects and, thus, need to be defined clearly. Unfortunately requirements often are not prioritised systematically. As a consequence, it is not determined in the early phases of a project which functions (or functional requirements) are going to be covered by which release. This paper suggests a technique to prioritise requirements and to assign them to software releases. Special emphasis is given on the fact that cost and benefit of each functional requirement are taken into consideration before a decision is taken.