CUIML, the Cooperative User Interfaces Markup Language, was developed as part of the DWARF project. The goal of DWARF is the development of a framework for augmented reality applications running on wearable computers. For wearable systems, the HCI (human-computer interface) consists of numerous I/O devices such as head mounted displays, palm-size devices, and speech recognition systems. This should lead to a multimodal interaction with the user. To make the development of multimodal user interfaces easier, we propose a unified user interface description language. This language describes the user interface in an abstract way and allows to map it to different output and input components. To keep the different parts of the user interface in a consistent state, a controller object is needed.