This article presents the conceptual connectors existing between the legitimating contractualist model of democracy and the legal theory of contract. An analysis of such connections is proposed to approach to the current concepts of democracy, popular sovereignty, freedom and law. Through a historical-comparative approach, the paper tries to use the legal theory of contract to reformulate the problem of the current legitimation of democracy. This proposal is based on the reminder that, from Roman law, public order constitutes a limit to contractual freedom, as to all forms of freedom; it also proposes a context to rethink political freedom in light of the reinterpretation that has been given to contractual freedom by virtue of its constitutionalisation, and the way in which it has been balanced with imperatives such as safeguarding the legal order and fundamental rights.