Response inhibition is the most basic form of behavioral control, which can occur either proactively to anticipate known task requirements, or reactively in response to sudden changes in the environment. This review will highlight some of the recent progress that has been made in understanding the mechanisms of response inhibition. Neurophysiological experiments in primates and rodents have uncovered a common neural network underlying reactive motor control. However, important questions regarding the exact locus of inhibitory control are still open. Other experiments have begun to investigate proactive control mechanisms in the medial frontal cortex. Proactive control might have a more general function in behavioral control by regulating speed-accuracy tradeoffs and the urgency to make a decision.