 Like most other ancient philosophers, Plato maintains a virtue-based eudaemonistic conception of ethics. That is to say, happiness or well-being (eudaimonia) is the highest aim of moral thought and conduct, and the virtues (aretê: ‘excellence’) are the requisite skills and dispositions needed to attain it. If Plato’s conception of happiness is elusive and his support for a morality of happiness seems somewhat subdued, there are several reasons. First, he nowhere defines the concept or makes it the direct target of investigation, but introduces it in an oblique way in the pursuit of other questions. Second, the treatment of the human good varies in the different dialogues, so that readers find themselves confronted with the problem of what to make of the discrepancies in different works. This touches on a fundamental problem with Plato’s work – namely whether to follow a ‘unitarian’, ‘revisionist’, or ‘developmentalist’ approach to Plato’s writings. Whereas unitarians regard the dialogues as pieces of one mosaic, and take the view that Plato in essence maintains a unified doctrine from his earliest to his latest works, revisionists maintain that Plato’s thought underwent a fundamental transformation later in his life, while ‘developmentalist’ hold that Plato’s views evolved significantly throughout his career. While revisionism has lost its impact in recent years, developmentalism has gained in influence. Although there is no unanimity, few unitarians deny nowadays that the character of Plato’s early, middle, and late works differ in style, language, scope and content, as is to be expected in a philosopher who worked for more than fifty years. Most developmentalists, in turn, agree that it is impossible to line up Plato’s works like pearls on a string and to reconstruct his progress from dialogue to dialogue; for example, where the views expressed in different dialogues seem to disagree there may be complementation or supplementation at work, rather than divergence. Given that Plato never speaks in his own voice, it is important to take note of who the interlocutors are and what role is assigned to Socrates, if he is the main speaker. Plato’s dialogues should never be treated in isolation when it comes to the reconstruction of his doctrine; but even the comparison and contrasting of ideas presented in different dialogues is not a sure recipe for interpreting this elusive thinker’s views. 