"In the 600s there were local issues of paper currency in China and by 960 the Song Dynasty, short of copper for striking coins, issued the first generally circulating notes. A note is a promise to redeem later for some other object of value, usually specie. The issue of credit notes is often for a limited duration, and at some discount to the promised amount later. The jiaozi nevertheless did not replace coins during the Song Dynasty; paper money was used alongside the coins" (Wikipedia article on Banknote, accessed 08-13-2009).
Carter, Invention of Printing in China 2nd ed 103-04.