The author describes Mobi-D (Model-Based Interface Designer), a comprehensive environment that supports user-centered design through model-based interface development. In the Mobi-D paradigm, a series of declarative models, such as user-task, dialog, and presentation, are interrelated to provide a formal representation of an interface design. This contrasts to model-based systems, which use only one or two models in isolation and have no explicit notion as to how the various model elements are organized into an interface design.