This chapter looks at ‘Twin Peaks’, not as distinct supervisory entities with reasonably well-defined responsibilities, as this is covered elsewhere in this book. Rather, it looks at the supervision of a concept ‘that must be considered by both ‘peaks’ – that of ‘culture’ and, in particular, ‘macro-culture’. The chapter concludes by pointing out that the ‘Twin Peaks’ are not independent but sit on shared foothills, beset by common problems – in this case, the need to understand the various ‘cultures’ of the individual firms that both peaks supervise. It makes little sense for one regulator to measure and try to ‘influence’ cultures in one way in a firm if another supervisor uses different definitions, measures and influencing mechanisms for the same firm. At the very least, there is a need for regulators to come to a shared understanding of problems that they have in common, such as how to influence the cultures of firms that they supervise. The chapter proposes a novel approach to addressing this quite complex problem.