Aggressive behavior is a basic form of human social interaction, yet little is known about its neural substrates. We used a laboratory task to investigate the neural correlates of reactive aggression using functional magnetic resonance imaging. The task is disguised as a reaction-time competition between the subject and two opponents and entitles the winner to punish the loser. It seeks to elicit aggression by provocation of the subject. As each single trial in this task is separated into a decision phase, during which the severity of the prospective punishment of the opponent is set, and an outcome phase, during which the actual punishment is applied or received, the paradigm enables us to analyze the neural events during each of these phases. Specific neural responses in areas related to negative affect, cognitive control and reward processing provide additional information about the cognitive, emotional and motivational processes underlying reactive aggressive behavior and afford us with the possibility to test and expand theories on aggression such as the General Aggression Model.