This chapter investigates Thucydides’ views about morality and justice and the role that these concepts play in his work. It argues that Thucydides’ own ideas about justice were conventional, but that his understanding of the role of justice in shaping human affairs was more novel. The chapter explores the methodological problem of reconstructing Thucydides’ views about justice and morality, given that most statements on these themes are made by characters rather than the author. It then analyses the text’s representation of key ideas about justice, morality and other virtues; it explores how these are manifested in Thucydides’ characterization of individuals in the work; and it surveys the differences between Thucydides’ representation of Spartan and Athenian approaches to justice and morality.