"From 1260, when Kublai Khan completed the conquest of China and took the title of emperor, the issue of paper money became a settled and permanent feature of the Mongol government's financial policy. . . . Records have been preserved showing year by year the amount of notes issued through Kublai's reign and that of his successors for ninety-seventy years (1260-1356)" (Carter, Invention of Printing in China 2nd ed  107).
"Paper money was the first form of Chinese printing met with by European travelers, was independently discussed by at least eight pre-Renaissance European writers, and, so far as is known, is the only form of Chinese printing described in European writings of pre-Gutenberg days. Marco Polo's description is the most detailed" (Carter, op. cit., 109).
Marco Polo described the use of paper currency throughout Khubilai Khan’s Yuan dynasty:
"With these pieces of paper, made as I have described, he [Khubilai Khan] causes all payments on his own account to be made; and he makes them to pass current universally over all his kingdoms and provinces and territories, and whithersoever his power and sovereignty extends. And nobody, however important he may think himself, dares to refuse them on pain of death. And indeed everybody takes them readily, for wheresoever a person may go throughout the Great Kaan’s dominions he shall find these pieces of paper current, and shall be able to transact all sales and purchases of goods by means of them just as well as if they were coins of pure gold. And all the while they are so light that ten bezants’ worth does not weigh one golden bezant.
"Furthermore all merchants arriving from India or other countries, and bringing with them gold or silver or gems and pearls, are prohibited from selling to any one but the Emperor. He has twelve experts chosen for this business, men of shrewdness and experience in such affairs; these appraise the articles, and the Emperor then pays a liberal price for them in those pieces of paper. The merchants accept his price readily, for in the first place they would not get so good a one from anybody else, and secondly they are paid without any delay. And with this paper-money they can buy what they like anywhere over the Empire, whilst it is also vastly lighter to carry about on their journeys. And it is a truth that the merchants will several times in the year bring wares to the amount of 400,000 bezants, and the Grand Sire pays for all in that paper. So he buys such a quantity of those precious things every year that his treasure is endless, whilst all the time the money he pays away costs him nothing at all. Moreover, several times in the year proclamation is made through the city that anyone who may have gold or silver or gems or pearls, by taking them to the Mint shall get a handsome price for them. And the owners are glad to do this, because they would find no other purchaser give so large a price. Thus the quantity they bring in is marvellous, though these who do not choose to do so may let it alone. Still, in this way, nearly all the valuables in the country come into the Kaan’s possession" (Marco Polo and Rustichello of Pisa, “Book Second, Part I, Chapter XXIV: How the Great Kaan Causeth the Bark of Trees, Made into Something Like Paper, to Pass for Money over All His Country,” in The Book of Ser Marco Polo: The Venetian Concerning Kingdoms and Marvels of the East, translated and edited by Colonel Sir Henry Yule, Volume 1 (London: John Murray, 1903).