This doctoral dissertation aims to elucidate this main research question: To what extent does the Spanish constitutional debate of 1931 show conceptual innovation in the parliamentary context? Parliamentary deliberations around constitutional drafts delve into alternative views on the foundations of a new state, in this case a democratic state. There, concepts express not just the ideological differences between political options, but also the social, political and economic concerns of a new historical time. Constitutional debates involve an extensive number of political and legal knowledge whose intellectual references are usually found in different schools of political thinking and philosophical ideas. Alternative viewpoints, often hardly compatible, about fundamental rights and the state are contrasted in parliamentary deliberations. As a result, divergent and disputed understandings of concepts are visible. Parliamentary constitutional deliberations, unlike other kind of parliamentary debates, reflect intellectual references in the context of constitutional debates in a constituent assembly. They link international with national practices on constitution-making. There, all kind of resources, from rhetorical skills to public law, history of political thought and political theory arguments are present. Together, they shape the foundations of a new political regime. With this backdrop, this research takes the debates of the Spanish Constituent Assembly (Cortes Constituyentes) of 1931 as an indispensable reference for legislative production in the context of a new democratic regime and an instance of innovative use of political concepts and ideas. That way it analyzes a selection of some of the nuclear themes of political theory (controversies around the meanings of basic rights and freedoms, the state, legitimacy, justice or property, among others) conceptualized through parliamentary deliberations. In this research, conceptual history, political theory and parliamentary constitutional history are regarded as complementary disciplines. Combining their methodological perspectives, the disputed parliamentary meanings of ideas, such as state, reform, revolution, sovereignty, freedom of conscience, property rights and semi-parliamentarism are revealed. Furthermore, the analysis of these concepts brings to light the main features of conceptual development in the Spanish Constituent Assembly of 1931. Keywords: Spanish constitutional debate of 1931, political theory, conceptual history, parliamentary deliberation, political rhetoric