Abstract: In the late twentieth century constitution-designers came to understand that, in addition to the three classic Montesquiean functions of law-making, law-applying, and law-interpreting, constitutional institutions had to perform an additional function, that of protecting the constitution itself. That function is performed by constitutional courts, but also by agencies concerned with elections and with corruption. A case study of an important anti-corruption inquiry in South Africa illustrates the proposition that institutions protecting the constitution must combine independence from other political actors with some degree of accountability to them. Following the case study, the Article examines some general characteristics of these institutions, sketching some of the questions about independence and accountability that constitution-designers must consider. Among those questions are the possibility of too much independence, with the institutions having a greater impact on political outcomes than is appropriate, too much responsiveness to non-political but professional concerns such as legality and the details of accounting conventions, and of course too much accountability to the very political institutions that these agencies are designed to regulate. Throughout the Article emphasizes the role of conflicts of interest both in setting the agenda for these agencies and in posing the risk that the agencies will undermine rather than protect the constitution.