Jiaozi (currency) in the context of "String of cash coins (currency unit)"

Paper money, often referred to as a note or a bill (North American English), is a type of negotiable promissory note that is payable to the bearer on demand, making it a form of currency. The main types of paper money are government notes, which are directly issued by political authorities, and banknotes issued by banks, namely banks of issue including central banks. In some cases, paper money may be issued by other entities than governments or banks, for example merchants in pre-modern China and Japan. "Banknote" is often used synonymously for paper money, not least by collectors, but in a narrow sense banknotes are only the subset of paper money that is issued by banks.

Paper money is often, but not always, legal tender, meaning that courts of law are required to recognize them as satisfactory payment of money debts.

The Song dynasty (Chinese: 宋朝; 960–1279 CE) witnessed many substantial scientific and technological advances in Chinese history. Some of these advances and innovations were the products of talented statesmen and scholar-officials drafted by the government through imperial examinations. Shen Kuo (1031–1095), author of the Dream Pool Essays, is a prime example, an inventor and pioneering figure who introduced many new advances in Chinese astronomy and mathematics, establishing the concept of true north in the first known experiments with the magnetic compass. However, commoner craftsmen such as Bi Sheng (972–1051), the inventor of movable type printing (in a form predating the printing press of Johannes Gutenberg), were also heavily involved in technical innovations.

The ingenuity of advanced mechanical engineering had a long tradition in China. The Song engineer Su Song, who constructed a hydraulically-powered astronomical clocktower, admitted that he and his contemporaries were building upon the achievements of the ancients such as Zhang Heng (78–139), an astronomer, inventor, and early master of mechanical gears whose armillary sphere was automatically rotated by a waterwheel and clepsydra timer. The application of movable type printing advanced the already widespread use of woodblock printing to educate and amuse Confucian students and the masses. The application of new weapons employing the use of gunpowder enabled the Song to ward off its militant enemies—the Liao, Western Xia, and Jin with weapons such as cannons—until its collapse to the Mongol forces of Kublai Khan in the late 13th century.