This dissertation examines the relationship between law and virtue in Plato’s Laws. In the introductory part, I sketch a general picture of the legislative perfectionism in the Laws, showing that Plato takes promoting the virtue of citizens to be a specifically legislative task. I also point out some ways in which Aristotle is drawn toward perfectionist legislative ideals. In the first part, I discuss the psychology of virtue and the pervasiveness of law. I offer a novel interpretation of the psychology of virtue according to which virtue involves psychic harmony and conflict between various aspects of an integrated person. This view makes essential reference to certain aspects of the Laws’ political theory. For law provides various frameworks within which one’s habits are formed, it is the mechanism through which citizens receive virtue-conferring evaluative information, and its influence is meant to be causally efficacious in situations of deliberative tension. Part two considers how citizens of Magnesia improve intellectually and in their evaluative outlook by living in a city strictly structured by laws. I examine various features of the laws and preludes and offer a new interpretation of how these contribute to moral development through a method I call proleptic engagement. I also examine the extra-legal venues through which citizens can enhance their understanding and appreciation of the virtuous ways of life required by law, and explain the entrenching impact this has on the beliefs and values citizens acquire through their upbringing and training. Part three discusses the role of law in early moral development for Aristotle. In contrast to the popular ‘role model’ view of early moral development, where the transmission of reasons from persons is seen to play a key role, I argue that law is a much better candidate for accomplishing what Aristotle hopes early habituation can accomplish. I explain the criteria that are most conducive to correct habituation, and show that the law meets these criteria in ways that are ideally conducive to moral progress.