In all primates, the cortical control of hand and arm movements is initiated and controlled by a network of cortical regions including primary motor cortex (M1), premotor cortex (PMC), and posterior parietal cortex (PPC). These interconnected regions are influenced by inputs from especially visual and somatosensory cortical areas, and prefrontal cortex. Here we discuss recent evidence showing M1, PMC, and PPC can be subdivided into a number of functional zones or domains, including several that participate in guiding and controlling hand and arm movements. Functional zones can be defined by the movement sequences evoked by microstimulation within them, and functional zones related to the same type of movement in all three cortical regions are interconnected. The inactivation of a functional zone in each of the regions has a different impact on motor behavior. Finally, there is considerable plasticity within the networks so that behavioral recoveries can occur after damage to functional zones within a network.