Complex dialogs with comprehensive underlying data models are gaining increasing importance in today's Web applications. This in turn accelerates the need for highly dynamic dialogs offering guidance to the users and thus reducing cognitive overload. Beyond that, requirements from the fields of aesthetics, Web accessibility, platform-independence, and Web service integration arise. To this end, we present an evolutionary, extensible approach for the model-driven construction of advanced dialogs. It is based on a Domain-specific Language (DSL) focusing on simplicity and fostering collaboration with stakeholders. Categories and Subject Descriptors D.2.2 [Software Engineering]: Design Tools and Techniques ? User Interfaces, Evolutionary Prototyping, Petri nets. D.2.13 [Software Engineering]: Reusable Software ? Domain Engineering. General Terms Design, Human Factors, Languages. Keywords Web Engineering, User Interaction, DSL, Model-driven.