The work described here aims to isolate the component processes of decision making that rely critically on particular subregions of the human prefrontal cortex, with a particular focus on the orbitofrontal cortex. Here, experiments isolating specific aspects of decision making, using very simple preference judgment and reinforcement learning paradigms, were carried out in patients with focal frontal damage. The orbitofrontal cortex and the adjacent ventromedial prefrontal cortex play a critical role in decisions based on subjective value, across many categories of stimuli, and in learning to choose between stimuli based on value feedback. However, these regions are not required for learning to choose between actions based on feedback, which instead seems to rely critically on the dorsomedial prefrontal cortex. These results point to a potentially common role for the orbitofrontal cortex in representing the context-sensitive, subjective value of stimuli to allow consistent choices between them. They also argue for multiple, parallel, value-based processes that influence behavior through dissociable mechanisms.