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The number and the diffusion of non traditional devices able to provide every-where and any time access to the Web is increasing day by day. These devices include not only cellular phones, PDAs, and terminals for disabled people, but also new kind of devices, possibly embedded into tools such as household appliances, or vehicle dashboards. The characteristics of the various devices are so different that the issues related to the delivering of information and services on the Web do not involve only the presentation aspects, but structural and navigational aspects as well. As an example consider a cellular phone: its limited computing capabilities require that information is filtered and organized as a collection of atomic units whose dimensions depend closely on specific features of the device. It turns out that a novel and fundamental requirement in this scenario is the ability of the system to adapt and personalize content delivery according to the context of the client (a human being or an application). There is no accepted definition of context, but the term is a usually adopted to indicate “a set of attributes that characterizes the capabilities of the access mechanism, the preferences of the user and other aspects of the context into which a Web page is to be delivered”. These may include the access device (even in presence of strong heterogeneity of devices), the network QoS, the user preferences, the location, the time, the language, and so on. Therefore adaptiveness usually concerns several independent coordinates. In this chapter we present models, methods and techniques for the design and the development of Web-based information systems, which are adaptive with respect to context information.