A wireless pervasive computing environment needs to dynamically adapt its functionality and behaviour to changes in the resources and services available to a user at any point in time. For a mobile user this means that as the user changes location, the pervasive environment should take account of any changes to the services that are available. Thus initially when the user requests a service the most appropriate service must be provided, but as the user moves around, the service provided could change. To handle this, a wireless pervasive system needs to provide dynamic service composition (and re-composition) based on the user's personal preferences and current context. The Daidalos project is developing a platform to support pervasive services, which provides dynamic personalized service composition. This paper describes the problems and the role of personalization in the approaches adopted in Daidalos to deal with dynamic service composition and re-composition. The basic ideas have been prototyped and demonstrated, and are currently being integrated and extended.