Usability tests are commonly used in industry to identify shortcomings and weaknesses in consumer product design before the product is being launched on the market. A usability test models the usage situation, in which users are asked to carry out a set of tasks with a consumer product (e.g., coffee machine) to see what problems the user has encountered during product operation. Previous research has indicated remarkable inconsistencies across usability tests with regard to the usability problems being identified. The present project aims to identify factors that have an influence on test outcomes with a view to increase the effectiveness and utility of usability tests. Factors that are expected to have an influence are, for example, presence of observers, product aesthetics, and the kind of prototype used (e.g., paper prototype, computer simulation). In a series of experiments carried out in a usability laboratory but also in people’s homes, the influence of these factors is tested by comparing several conditions (e.g., one group of users operates an attractively designed prototype while the other group operates an unattractive one). The research is carried out with a range of typical consumer products, such as mobile phone, digital camera and coffee machines. This also allows us to determine the generalisability of the effects across a certain type of product (e.g., products with high and low prestige value). Finally, the project aims to examine the transferability of the findings from the domain of consumer product to a work context (e.g., is the influence of aesthetics on perceived product usability lower when a mobile phone is used at work than at home?). On the basis of the findings of the project, we will be able to provide some recommendations to practitioners involved in usability testing about how they can improve their procedure to conduct a usability test.