This study deals with the engineering of Web Information Systems (WIS) which are adaptable to their users. Like every Information System supporting the organization's functioning, a WIS has to provide its users with functionalities for efficiently processing information. In such Web-based systems, functionalities are generally proposed through an hypermedia interface whose structure is a composition of nodes related by navigational links. Such a large amount of functionalities and information accessible through this hypermedia can lead to some disorientation or cognitive overload syndromes experienced by the users. It is therefore crucial to adapt to users the functionalities, the content and the presentation of information to limit these negative effects. We address this issue by introducing and implementing the notion of Progressive Access into a WIS design approach. Our objective is to offer the WIS design the possibility to build a WIS which has the capacity to deliver progressively a personalized information to its end users. First, information considered as essential with regard to their needs is provided, and then, some additional information, if needed, is gradually available through navigation mechanisms. The Progressive Access Model (PAM) describes the concepts and mechanisms of our proposition. The PAM is general enough to apply to different application domains expressed using different representation formalisms (E/R, object, XML,...). This model is central in our design approach. The PAM is closely related to four other models (Data Model, Functional Model, Hypermedia Model, User Model). We show how these five models are exploited during the design phase leading to the generation of WIS which dynamically adapt content, presentation and progressive access features to theirs users. Both the design and the generation of such systems are supported by a platform called KIWIS (Knowledge for Improving Web Information Systems) which validates the progressive access approach.