This paper discusses platform independent Web application modeling and development in the context of model-driven engineering. A specific metamodel (and associated notation) is introduced and motivated for the modeling of dynamic Web specific concerns. Web applications are represented via three independent but related models (business, hypertext and presentation). A kind of action language (based on OCL and Java) is used all over these models to write methods and actions, specify constraints and express conditions. The concepts described in the paper have been implemented in the Netsilon tool and operational model-driven Web information systems have been successfully deployed by translation from abstract models to platform specific models.