Ethics – the philosophical consideration of the question how we should live – is central to Plato's thought throughout his career. His thought, like that of many ancient philosophers, focuses especially on the virtues – that is, on morally admirable states of soul or character – rather than on the rightness or wrongness of specific actions, although he does, of course, sometimes consider the way the virtues are expressed in action.

While Plato devoted many dialogues to ethical questions, most of them are normally seen as Socratic dialogues, expressing the thought of Socrates rather than of Plato himself. The work in which the mature Plato presents his ethical ideas most fully is the Republic. Its official theme is justice, but as justice is seen as bound up with the other virtues, it does in fact present Plato's thought about the virtues more generally.

Plato continued to think about ethical issues later in his career; as we have seen, two later works, the Statesman and Laws, deal primarily with political topics, but these are, of course, bound up with ethical ones in Plato's thought, especially as he sees the promotion of virtue as a major part of the work of government. He also wrote one more work that deals directly with ethical questions, the Philebus (the last of his dialogues to feature Socrates as chief speaker); this addresses, rather more directly than the Republic, issues about the good or happy life for human beings (rather than about virtue), and considers the place of pleasure and knowledge in the good life.