Throughout his political works, Plato takes the aim of politics to be the virtue and happiness of the citizens and the unity of the city. This paper examines the roles played by law in promoting individual virtue and civic unity in the Republic, Statesman, and Laws. Section 1 argues that in the Republic, laws regulate important institutions, such as education, property, and family, and thereby creating a way of life that conduces to virtue and unity. Section 2 argues that in the Statesman, the political expert determines the mean between extremes and communicates it to citizens through laws that guide their judgment and conduct, so that they become virtuous themselves and the city is unified; this account of the role of law suggest how even non-expert legislation can contribute to virtue and unity. Section 3 argues that the Laws affirms and develops the idea that citizens should know and accept the laws to become virtuous themselves and to unify the city, and explains how the persuasive preludes and the sanction for violation attached to laws contribute to citizen virtue and civic unity.