Three basic themes interest central banks and their counsel: (i) monetary policy, (ii) banks and bank supervision, and (iii) the payment system. The third theme is the focus of Chapters 4 and 5. The payment system can be analogized to the circulatory system of an organism, the life blood that keeps the world’s economic organism healthy and operating. If this analogy is correct, a loss of confidence in the payment system may cause other destructive effects in the world’s economy. Such effects might include a breakdown in commerce, a cessation in commercial transactions, or an economic stagnation that would be of great concern to central banks and central bank counsel.