Reforming the UK’s corporation tax code is becoming more of a widespread political concern than the preoccupation of specialists. This functionalist study offers an interpretation, and assesses the arguments. It views the corporation tax code as public law, energised by political values whose meaning and prioritisation are shaped by the prudential logic of effectiveness. The institutions that generate the code, and the challenges of globalisation to the nation state, have highlighted historic tensions between Crown and Parliament, and the latter’s scrutiny of the managerialist governance style that the code’s reform involves. This style is apparent in the ideology of the public interest that reform is designed to promote, a process that involves the skilful balancing of efficiency and fairness. Surprisingly, perhaps, there is little in the conduct of reform that violates the traditions of the UK’s representative democracy. The result is a code that, given its public law status, is a pre-eminent example of political jurisprudence. Its values, their prioritisation, and their change and complexity, are inevitably contentious, because they are the products of representative institutions. Criticism of the code generally understates these points. What are presented as impartial legal arguments are often simply rival views of the public interest.