Regulation is a pervasive feature of contemporary capitalism. How to ensure, in democratic states, that those to whom regulatory power and functions have has been delegated act in line with constitutional norms and values is a perennial, and much explored, question. This chapter seeks to do two things: first to set out a framework for analysing regulatory systems, and second, to use that framework to explore how constitutional actors seek to regulate, or more specifically to constitutionalise, the regulators they have created. In using a regulatory framework to analyse this element of constitutional systems, it thus proposes to ‘flip’ the usual perspective, and not just look (down) at regulatory systems from a constitutional perspective, but also look (up) at constitutions from a regulatory perspective. This flipped perspective will be used to conceptualise constitutions not from the starting point of established constitutional, legal or political theory but from a particular regulatory theory, that of decentred or polycentric regulation, and to explore the different ways in which ‘regulators are regulated’ through the interplay of the constitutional governance system with the regulatory systems it creates: through the goals and values each seeks to pursue, the techniques, organisations and individuals through which each acts, the particular sets of ideas or cognitive and epistemological frameworks those actors bring, and with a continual need both for, and in constant pursuit of, trust and legitimacy in the eyes of those on whose behalf they purport to govern.