BeatBender is a computer music project that explores a new method for generating emergent rhythmic drum patterns using the subsumption architecture. Rather than explicitly coding symbolic intelligence into the system using procedural algorithms, BeatBender uses a behavior-based model to elicit emergent rhythmic output from six autonomous agents. From an artistic perspective, the rules used to define the agent behavior provide a simple but original composition language. This language allows the composer to express simple and meaningful constraints that direct the behavior of the agent-percussionists. From these simple rules emerge unexpected behavioral interactions that direct the formation of complex rhythmic output. What is striking is that these rhythmic patterns, whose complexity is beyond human grasp, are both musically interesting and aesthetically pleasing. The output from the system is evaluated using both subjective and objective criteria to assess degrees of complexity, conve...