More than ever before, states conduct their business -- economic, political, security -- in or around multilateral forums. Institutions such as the United Nations, the World Trade Organization, and NATO are not only locations where states can negotiate but also repositories of widely shared rules and norms. Drawing on the views of scholars and practitioners, this study tracks the way multilateralism has moved beyond the state system to include nonstate actors and an expanding array of issues. Several of the chapters outline the deep shifts in thinking about anarchy and order, arguing that multilateralism is increasingly a value-laden norm about the virtues of rule-based global governance. Other chapters look at the actual operation of multilateral systems of rules, as states grapple with rogue regimes, nuclear proliferation, economic crises, and human rights abuses. The book's most interesting theme is that multilateralism -- as a form of organization -- has evolved from its origins as a set of principles for the conduct of diplomacy among sovereign states into a set of tools used to gain some control over a dangerously ungovernable world that exists beyond the state system.