The target article reviews studies of human cerebellar functional imaging and ablation in motor learning. This material is integrated with anatomical and physiological work in laboratory animals. A synthesis is presented as a working hypothesis on how the cerebellum might adapt, learn, and coordinate movement. An attempt is made to extend the motor role to certain mental operations, particularly those associated with mental movement. These notions met with varying enthusiasm. A few commentators seemed pleased with the overall result and offered supportive ideas. Some were critical of the proposed contributions to cognition and motor learning. A surprising number insisted that the cerebellum was more concerned with sensory processing than with movement management. Some thought we know too little to attempt such a synthesis.