This diploma thesis deals with aspects of a methodical approach to integrate usability engineering and software engineering. Based on a process model of usability engineering it is described what needs to be done in a user-centred process of software development, particularly during the analytical and constructive preparation of development projects. The process model of usability engineering is described following the V-model, which is a recognized software-engineering process model in Germany. The V-model has been extended and modified by the usability process model. Pertinent international standards have been considered, such as ISO 13407, ISO 12207, and ISO 9241. In practicing the usability-engineering process model it turned out that this approach is beneficial for ensuring the product's usability. Moreover, development projects could be accomplished within time and budget constraints, due to the better preparation of the projects. Usability will become a key competitive factor in the software market, since the more mature customers and users will no longer be satisfied with a product that merely works correctly and reliably. The software development process should be well prepared for that challenge.