Already controversially this statement suggests that the law thinks, and that it thinks about itself: to cast the law as both agent and object of scrutiny, it has been objected, involves a circularity that does not allow scrutiny to get off the ground. In this chapter we will treat the circularity not simply as productive but as constitutive of the meaning of the ‘constitutional’ as autopoietic. To answer the ‘epistemological’ objection we will follow Luhmann in his theory of how legal meaning is generated, and we will navigate (and also circumvent) a great deal of theoretical complexity, in order to arrive at an understanding of how legal operations at the first-order are controlled at the second-order, constitutional level, in the way in which they are organised, framed, sanctioned and reflected on, and thus how constitutional meaning is generated across all three dimensions: social, material and temporal. This, I will argue, is what systems theory may offer constitutional thinking that in the face of globalisation sweeping away the constitutional givens, finds it so extraordinarily difficult to answer its identity problem, the question ‘what is the Constitution?’ The answers we get range from theoretical a prioris, to unsustainable assumptions about constitutional culture, to meaningless zero-sum contrasts between political and legal constitutionalism, to weak and tentative delineations couched in the language of so many pluralisms and of a creeping constitutionalisation, all of which surrender the political dimension of the constitution and belie what the constitution is so obviously about: unity, framing, entrenchment, foundation, fixity, orientation and rationalisation.