This book is about the role of agents in policy and institutional change. It draws on cross-country case studies. The focus on ‘agency’ has been an important development, enabling researchers to better reveal the causal mechanisms generating institutional change (i.e., how institutional change actually takes place). However, past research has generally been limited to specific intellectual silos or scholarly domains of inquiry. Policy scholars, for example, have tended to focus on the various mechanisms and levels at which agency operates, drawing on institutionalist perspectives but not always actively contributing to institutionalist theory. Institutionalist perspectives, by contrast, have tended to operate at macro-levels of enquiry, embracing the ontological primacy of institutions in processes of isomorphism but not necessarily contributing to or embracing policy perspectives that engage in more granular analyses of policy making processes, implementation, and the instantiation of institutional and policy change. Despite the obvious complementarities of these two intellectual traditions, it is surprising how little collaborative work, or indeed cross fertilization of theory and analytical design has occurred. The core novelty of this volume is thus its focus on agential actors within institutional settings and processes of entrepreneurship that facilitate isomorphism and policy change. The book’s theoretical framework is grounded in variants of institutional theory, especially historical, sociological and organisational institutionalism and policy entrepreneurship literature. The overall conclusion is that that both institutionalists and public policy scholars have largely overlooked the importance of complex interactions between interdependent structures, institutions, and agents in processes of institutional and policy change.