A new discipline, Usability Design, is proposed as an extension to Rational Unified Process (RUP). The aim is to make RUP more user-centred. The discipline springs out of best practices for user-centred design and contains activities that have been carefully tested. Five new roles are introduced to take responsibility for the different activities. An example is given to show the content of the workflow, the workflow details and the activities. The Usability Design discipline help projects to focus on usability and the users throughout the system development lifecycle.