Jonathan Blake and Nils Gilman propose a new framework for global governance they call 'planetary subsidiarity.' Their argument begins with a recognition: nation-states, however powerful, are inadequate for managing challenges like climate change, pandemics, and biodiversity loss that operate at planetary scale. But global government is neither feasible nor desirable. The authors offer a middle path that assigns problems to the lowest level of governance capable of addressing them effectively, while creating robust mechanisms for coordination on truly planetary issues. Blake is a political theorist; Gilman leads the Berggruen Institute's Future of Capitalism program. Together they combine philosophical rigor with practical policy expertise. The book examines historical precedents for multilevel governance and current experiments in global coordination, assessing what works and what doesn't. They are honest about the political obstacles to their proposals while arguing that necessity may create openings that seemed impossible before. The writing is accessible despite the complexity of the subject matter, aimed at readers who sense that our current institutional arrangements are inadequate but aren't sure what alternatives exist. This is a serious contribution to thinking about humanity's collective future.