This thesis presents an unusual application of user modelling, the domain of interest being the physical abilities of a user. Specifically, a model which identifies aspects of keyboard use with which a user has difficulty is presented. An empirical study of keyboard and mouse use by people with and without motor disabilities is described. The study focuses on common input errors due to physical innacuracies in using these devices. For the majority of these errors, there exist keyboard or mouse configuration facilities intended to reduce or eliminate them. While such facilities are now integrated into the majority of modern operating systems, there is little published data describing their effect on keyboard or mouse usability. This thesis offers evidence that they can be extremely useful, even essential, but that further research and interface development are required. The user model focuses on four of the most commonly observed keyboard difficulties, and makes recommendations for settings for three keyboard configuration facilities. As a user modelling task, this application presents a number of interesting challenges for which traditional user modelling techniques are inadequate . The users to be modelled may tire easily, and may have cognitive disabilities in addition to physical ones. This makes it difficult to gain information by questioning users, or requiring them to perform given tasks. On shared machines many different users with very different requirements will be encountered, while individuals may also have varying requirements. This calls for a dynamic technique. This thesis attempts to show that it is feasable to draw accurate conclusions about a user's keyboard configuration requirements without questioning them, or requiring them to perform controlled tasks. The model presented records for a user's input unintrusively, and examines this input for evidence of physical errors or difficulties. Conclusions are based on the assumption that the user is typing English text. Any other textual language could be used.