Our human lives involve remarkable forms of practical organization: diachronic organization of individual activity, small-scale organization of shared action, and the organization of institutions. A theory of human action should help us understand these multiple forms of human practical organization and their interrelations. This book argues that a key is our capacity for planning agency. Drawing on earlier work on the roles of planning agency in the cross-temporal and small-scale social organization of our agency, this book focuses on the role of our planning agency within our organized institutions. It draws on ideas, inspired by H. L. A. Hart, that our organized institutions are rule-guided, and that to understand this we need a theory of social rules. This book draws on the planning theory of shared intention and the underlying theory of plan rationality to understand social rules. It understands an organized institution as involving authority-according social rules of procedure. It provides a model of organized institutions that makes room for pluralistic divergence. This leads to a model of institutional intention and—drawing on ideas from Harry Frankfurt—institutional intentional agency. The account charts a path between views of, among others, Kirk Ludwig, Philip Pettit, and Scott Shapiro. It sees our capacity for planning agency as a core capacity that underlies not only string quartets and informal social rules but also, thereby, the rule-guided structure of organized institutions and institutional agency. And it supports adjustments in views of mind, intention, and agency that are built into Donald Davidson’s field-shaping work.