Human societies have formalized instincts for compliance with reciprocal altruism in laws that sanction some aggression and not other aggression. Neuroscience makes steady advances toward measurements of various aspects of brain function pertinent to the aggressive behaviors that laws are designed to regulate. Consciousness, free will, rationality, intent, reality testing, empathy, moral reasoning, and capacity for self-control are somewhat subject to empirical assessment. The question becomes: how should law accommodate the wealth of information regarding these elements of mind that the science of aggression increasingly makes available? This essay discusses the evolutionary purpose of aggression, the evolutionary purpose of law, the problematic assumptions of the mens rea doctrine, and the prospects for applying the neuroscience of aggression toward the goal of equal justice for unequal minds. Nine other essays are introduced, demonstrating how each of them fits into the framework of the permanent debate about neuroscience and justice. It is concluded that advances in the science of human aggression will have vital, but biologically limited, impact on the provision of justice.