The paper argues that an ethos of experimentation is of central importance to contemporary neoliberal state politics – characterised by administrative decentralization, economic liberalization, infrastructural investment, and managerial government. Focusing primarily on the indeterminate and emergent forms of political life that take hold around processes of state decentralization in post-war Peru, the paper examines the complex politics of scale that mark relationships between diverse instances of the state. These emerge with particular clarity in infrastructure projects where attempts to reconfigure specific material and social relations confront conflicting competencies of national, regional and local agencies. A proliferation of technical instruments and norms are brought to bear in an attempt to contain the disruptive effects of such multiplicity. However, in practice, the diverse origins and orientations of these instruments and norms, foster ambiguity and uncertainty. State functionaries and citizens alike skilfully mobilize the multiple possibilities that the ambiguous regulatory frameworks offer them. But such attempts also reveal the precarious quality of the political, the arbitrary enactments of power and the techniques of differentiation that the ethos of experimentation also enables.