May 16, 2001 Systemically important payments systems are systems that, because of the size or the nature of the payments they process, could trigger or transmit serious shocks across domestic or international financial systems if they were insufficiently protected against risk. This article describes the overall framework of core principles developed for the design, operation, and oversight of such payments systems. The article reviews the role of the task force established to develop the core principles and examines the core principles themselves. It also examines the role of central banks in overseeing major payments systems and in applying the core principles to them. The focus is on the Bank of Canada's oversight responsibilities under the Payment Clearing and Settlement Act and on Canada's systemically important payments system—the LVTS.