This chapter deals with multilevel government as one of the significant themes of Paul Craig’s work. Its focus is multilevel government within the state, defined to include a range of forms of significantly devolved government, of which federation is one. The chapter responds to the apparent paradox that while multilevel government is now widely regarded as a desirable feature of a system of government, for many good reasons that include its potential to deepen democracy, multilevel systems tend to become increasingly centralised over time, detracting from the advantages they offer. The chapter suggests that a partial explanation lies in prevailing conceptions of constitutionalism, almost all of which were developed by reference to the assumptions of a unitary state. It argues instead for a concept of constitutionalism adapted to the objectives and circumstances of multilevel government, in a compound form that might be described as multilevel constitutionalism. Multilevel constitutionalism would not dictate the degree of devolution but it would support its adoption and operation once in place. Implementation of multilevel constitutionalism in turn demands cultural change on the part of the principal actors, to give it practical effect. The chapter explores what this might require of political elites in pursuing intergovernmental arrangements, and of courts, interpreting and applying the governing constitution. It concludes with still tentative suggestions about the extent to which a suitably modified version of multilevel constitutionalism could apply above the level of the state, to regional and international arrangements.