AbstractÐWhile task modeling and task-based design are entering into current practice in the design of interactive software applications, there is still a lack of tools supporting the development and analysis of task models. Such tools should provide developers with ways to represent tasks, including their attributes and objects and their temporal and semantic relationships, to easily create, analyze, and modify such representations and to simulate their dynamic behavior. In this paper, we present a tool, CTTE, that provides thorough support for developing and analyzing task models of cooperative applications, which can then be used to improve the design and evaluation of interactive software applications. We discuss how we have designed this environment and report on trials of its use. Index TermsÐTask models, models for interactive software systems, automatic tools for human-computer interaction, user interfaces.