Pluralist Constitutionalism challenges a foundational assumption of modern constitutional thought: that constitutional order depends on unity, hierarchy, and singular authority. Across diverse societies, however, constitutions are shaped by persistent forms of plurality, including competing legal authorities, overlapping constitutional identities, and multiple normative traditions. Yet constitutional theory has struggled to explain how such plurality can be sustained without collapsing into fragmentation or domination.Drawing on contemporary constitutional controversies and comparative analysis, this book argues that the central problem is not plurality itself, but the absence of a constitutional principle capable of structuring it. It advances semi-autonomy as that principle. Semi-autonomy provides the normative and institutional basis for sustaining plural authorities, identities, and legal systems within a shared constitutional framework, enabling them to coexist through bounded independence and ongoing interaction rather than hierarchy or exclusion.Developing a theory of pluralist constitutionalism, the book reconceives the constitution as a framework of mutuality in which recognition, reliance, and resistance structure relations among diverse constitutional actors. It then articulates a pluralist methodology for constitutional reasoning, showing how courts can engage overlapping legal authorities as co-constitutive sources of constitutional meaning through processes of identification, evaluation, and reconciliation. Through comparative case studies involving civil-indigenous legal systems, civil-religious legal systems, mixed jurisdictions, and federalism, this book demonstrates that pluralism is not an exceptional feature of constitutional orders, but a structural condition that depends on how institutions and courts organize and mediate normative diversity.This is an open access title. It is available to read and download as a free PDF version on Oxford Academic and is made available under a Creative Commons Attribution-Non Commercial-No Derivatives 4.0 International licence. It is free to read on Oxford Scholarship Online and offered as a free PDF download from OUP and selected open access locations.