The advent of multipolar administrative law poses challenges to the theory of administrative law. These consist in the growing disconnect between administrative law and the nation-state and the continuously close interaction, and at times fusion, of domestic and international administrative law and action, but also in the incremental dissolution of the public-private divide, the contribution of private actors to public governance, and the migration of administrative law ideas across legal orders. Administrative law is thereby placed in a transnational legal space and becomes subject to transnational legal processes. This also has repercussions on the theory of administrative law if the goal of such a theory is to provide an overarching framework for thinking about administrative law whenever and wherever administrative action occurs in times of the increasing detachment of its object from domestic legal sources and domestic public institutions. Such a theory, the paper argues, should take a transnational outlook that overarches domestic and international law and encompasses the idea that both public and private actors and instruments contribute to norm-generation in administrative law. The paper illustrates the idea of a transnational administrative law by looking at the law governing, and emerging from, cooperation between administrations and private actors through (public) contracts, such as public-private partnerships, concession agreements, or state contracts.