This article examines the fundamental role ‘reputable opinions’ play in Aristotle’s ethical epistemology. In the first part, the meaning of ‘endoxon’ is delineated with a view to Aristotle’s scattered remarks on the subject in his Topics as well as in his ethical writings. Based on this conceptual clarification, the second part of the paper offers a case study of the manner in which Aristotle uses endoxa in his treatment of the happy life (eudaimonia): Solon’s advice to refrain from calling someone happy before the end of his or her life is taken up by him in the Eudemian as well as in the Nicomachean Ethics in order to refine the definition and the conditions of happiness. The main aim of my analysis, among others, is a better understanding of what Aristotle means by tying the happiness of an agent to a ‘complete life’ (zôê teleia): In contrast to Solon, Aristotle does not intend to postpone the judgment of whether someone is happy until the end of his or her life, but emphasizes that virtuous activity must have already taken place for a while in order to justify the attribution of happiness to the agent in question. Based on this case study, the third part of the paper highlights the different ways in which Aristotle uses endoxa in his ethical writings. He treats them (1) as a potential source of knowledge, (2) as a methodical means of investigating disputed questions and (3) as a framework for anchoring his own concepts and definitions within a broader framework of a ‘reflective equilibrium’, which shows some resemblances to John Rawls’ ethical coherentism.