Recent years have witnessed a revival of interest in Benjamin Constant’s (1767-1830) political thought. Most contributions have started from the premise that Constant was a ‘liberal’, despite his own elusive use of the term. As a result, scholars have often interpreted Constant’s thought in ways that correspond to later conceptions associated with ‘liberalism’, sometimes with a not-so-thinly-veiled purpose of defending, through Constant, their own brand of liberalism. This dissertation attempts to avoid retrojections and partisan labelling, by focusing on Constant’s own political vocabulary. To this end, it concentrates on Constant’s all-pervasive use of the concept of ‘public opinion.’ The dissertation is divided into three main chapters, which unfold along chronological lines. The first chapter is devoted to the Directory period (1795-1799). The second chapter covers the years of Napoléon’s acme, from the fall of the Directory in 1799 to 1813. The third chapter focuses on the restoration period (1814-1830). This dissertation makes two central claims. It first argues that Constant used the concept of public opinion to offer an original answer to the question of political legitimacy. Rather than relying on the concept of popular sovereignty, as has been assumed, Constant described governments as being underpinned by the people’s opinion. When Constant talked about popular sovereignty, it was not to endorse it, but to urge that it should be disposed of in light of Napoléon’s rhetorical uses of the concept. According to Constant, both the limits and the source of political authority were set by the people’s changing beliefs – what they thought rulers were entitled to do, and on what basis. This sheds light on Constant’s shifting views on heredity and elections as the basis of political legitimacy, as well as his much commented-upon endorsement of constitutional monarchy after having championed a republic as the best form of government. Second, it shows that Constant’s understanding of representative government hinged on a specific conceptualization of the people’s power as public opinion, which was distinct from either popular sovereignty or national sovereignty. Constant believed that representatives ultimately always had the right to make binding decisions for the community. In order to avoid arbitrary, uninformed or out-of-touch collective decisions, Constant designed representative government as a receptacle of public opinion, understood as the reflection of the people’s interests. This sheds new light on Constant’s ideas about representation, the legislative mandate, and political liberty, as well as on his theory of the balance of branches of government, through which he planned to guarantee, as far as possible, the conformity between laws and public opinion.