||E-commerce and m-commerce have dramatically boosted the demand for services which enable ubiquitous access. Ubiquity with its anytime/anywhere/anymedia nature requiring context-aware computing, calls for new engineering techniques supporting these kind of services. In this document, we propose the notion of customisation as the uniform mechanism to adapt ubiquitous web applications towards a certain context. In particular, customisation is regarded as a new modelling dimension, influencing all other level of ubiquitous web application design. As a prerequisite for supporting customisation design, a set of generic models is introduced comprising a context model and a rule model, together with several sub models. At the application's side, a set of generic adaptation operations is provided which can be complemented by application specific ones. These adaptation operations can be integrated into the ubiquitous web application on the basis of adaptation hooks. A customisation toolkit in terms of a customisation rule editor and browser supports an integrated modelling process and facilitates reusability on the basis of a repository of customisation rules, macros and patterns. Finally, a process is introduced, covering the whole task of customisation design, with a special focus on reusability and the distinction between static and dynamic adaptation, herewith providing a holistic view on the development process of ubiquitous web applications.