Abstract. Rich Internet applications (RIAs) enable novel usage scenarios by overcoming the traditional paradigms of Web interaction. Conventional Web applications can be seen as reactive systems in which events are 1) produced by the user acting upon the browser HTML interface, and 2) processed by the server hosting the application state and logic. In RIAs, distribution of data and computation across client and server broadens the classes and features of the produced events as they can originate, be detected, notified, and processed in a variety of ways. In this work, we investigate how events can be explicitly described and coupled to the other concepts of a Web modeling language in order to specify collaborative Rich Internet applications.