This book offers a new argument for the ancient claim that well-being as the highest prudential good -- eudaimonia -- consists of happiness in a virtuous life. The argument takes into account recent work on happiness, well-being, and virtue, and defends a neo-Aristotelian conception of virtue as an integrated intellectual-emotional disposition that is limited in both scope and stability. This conception of virtue is argued to be widely-held and compatible with social and cognitive psychology. The main argument of the book is as follows: (i) the concept of well-being as the highest prudential good is internally coherent and widely held; (ii) well-being thus conceived requires an objectively worthwhile life; (iii) in turn, such a life requires autonomy and reality-orientation, i.e., a disposition to think for oneself, seek truth or understanding about important aspects of one's own life and human life in general, and act on this understanding when circumstances permit; (iv) to the extent that someone is successful in achieving understanding and acting on it, she is realistic, and to the extent that she is realistic, she is virtuous; (v) hence, well-being as the highest prudential good requires virtue. But complete virtue is impossible for both psychological and epistemic reasons, and this is one reason why complete well-being is impossible.