In the previous unit you explored various arguments for why user-centred design (or UCD) should be a central feature of interactive systems design. This unit will present an overview of the key UCD tools and practices and show how they relate to conventional systems development processes. UCD tools and techniques differ various ways including their viewpoint (e.g. cognitive psychology or computer science) , formality (e.g. compare evaluations by inspection with formal user modelling for instance), user involvement, when they are applied and deliverables.