The goals and thinking behind the doctrine of the separation of powers have proven to be so compelling that in virtually all democratic systems across the world, some version of the separation of powers concept has been enshrined in the constitution. The contributors to this volume were motivated by a recognition of the value that the doctrine has but also by the need to re-think its core aspects in light of recent changes both in design and practice. Much recent work has sought to develop new theoretical defenses or reconceptualize the purpose or functioning of the separation of powers. In contrast, this volume examines the evolution of the doctrine in light of important developments that we believe have been underexplored in existing work. First, the recent past has seen important changes in the field of constitutional design. These trends are most pronounced in what Daniel Bonilla has called the constitutions of the “global south,” but they are far from exclusive to new or more fragile democracies. These include questions about the changes in function of existing institutions in light of the inclusion of more expansive lists of rights such as socio-economic rights. They also include the widespread inclusion of independent accountability institutions – such as human rights commissions – whose place within the existing separation of powers is unclear. Secondly, a series of political and technological changes have altered the way the traditional model functions. While these shifts are difficult to generalize across countries, scholars have noted an increase in executive power and a decrease in legislative legitimacy and importance. The chapter examines the implications of these practical shifts for the theory of the separation of powers. Thirdly, we pose the question whether the differences between the constitutionalism that is developing in the global south and the traditional constitutionalism of the global north requires a divergent conception of the separation of powers, or whether a unified theoretical conception is possible. Lastly, we attempt to provide an understanding of how the various chapters in the book tackle the problems we examine.