This dissertation is a discussion of the many ambiguities surrounding Rousseau’s conception of happiness. In the first chapter, I expose Rousseau’s various conceptions of happiness in Émile. His main conception is offered at the beginning of Book II. Rousseau defines happiness as the equilibrium between desires and faculties. I show how this definition fits with his conception of human nature as it is developed in the Second Discours. Then I turn to a brief exposition of the alternative ideas of happiness that are exposed in the remaining of Émile. I also discuss various recent interpretations of Rousseau’s understanding of happiness. I turn to Rousseau’s autobiographical writings for the remaining chapters. The second chapter discusses Rousseau’s self-understanding of what made him miserable during his life. I focus on two episodes of his life: his break with the Parisian life and his crisis during the publication of Émile. I show how Rousseau often blames the circumstances or others for his unhappiness rather than his opinions or his heart. The last two chapters attempt to define what the happiness was that Rousseau experienced. The third chapter tries to understand what sort of solitude makes Rousseau happy, and if indeed he is happy in this situation. I explore why society is unsatisfying for him and whether his desire to be alone is coherent. The final chapter discusses the nature of Rousseau’s blissful rêveries. I show how melancholia appears to be at the center of his ecstasies in the second letter to Malesherbes. In the Fifth Walk of the Rêveries, however, Rousseau seems to settle for a quasi-lethargic experience. The minimal sentiment of his own existence he defines as happiness is compared to other blissful experiences described in the book. Finally, I discuss whether Rousseau needed to know the truth or to philosophize in order to be happy. In particular, I discuss his claim in the Third Walk to be in need of the doctrine of the Profession de foi du Vicaire savoyard to be happy. Rousseau’s sincerity is ambiguous. Its analysis unveils a few problems about his claims to be selfless and to have dedicated his life to the truth.