When was paper money first used?

In Tang-dynasty China (618–907), merchants began using paper certificates called 'flying cash' to avoid carrying heavy strings of coins. In the early 11th century, merchants in Sichuan issued notes called jiaozi, and the Song government took over their issue around 1024, creating the first government-issued paper money. Marco Polo later marvelled at the paper currency of the Yuan dynasty in the 13th century. Europe was slow to follow; Sweden's Stockholms Banco issued the first European banknotes in 1661. Today most banknotes are printed on cotton paper or polymer.