A growing range of applications can benefit from Distributed Virtual Environments (DVEs), from CAD to e-learning, and in a variety of sectors from entertainment to scientific simulations. Developing such projects is challenging because writing real-time software in computer graphics, distributed applications and behavioural simulations is technically difficult and because no comprehensive design methodologies have put the emphasis on the integration of complex and varied behaviours in distributed applications. We believe that by outlining the common mechanisms of behavioural simulation, by defining a model of communication between behavioural modules, and by implementing a scaleable framework for the composition and simulation of distributed behaviours, the task of the VR developer will be made easier, more focused and more robust.