Coin currency dates back thousands of years. But paper currency is a relatively new idea. The Tang (618–907) and Song (960–1279) Dynasties are credited with developing something like a paper money system where merchants exchanged coins for receipts of deposit. These notes were some of the earliest paper currencies. Later, the Song government issued the right for shops to create their own banknotes, and later took over these responsibilities, producing their own state-issued currency. During the same time period, the Islamic world was developing a currency system. Paper money in Europe wasn’t introduced until 1661 in Sweden.