We describe a VRML/Java-based virtual environment that is populated with heterogeneous articulated agents. In this simulated environment, agents compete for collecting certain objects while avoiding obstacles and other agents. Environment simulation, agent control, and visualization are distributed using a client/server approach. An important feature of the framework is its openness for novel kinds of agents: user defined agents can be integrated into the environment by supplying VRML models of the agents’ visual appearance and agent control clients that follow a predefined communication protocol. The environment serves as testbed for exploring principles for the design of autonomous, yet instructable agents. Instructability is necessary because agents represent human users. Autonomy is required so as to relieve the human from too much technical detail when directing the agent to approach and to pick up target objects with their manipulators. Autonomy is also necessary to enable t...