A string of cash coins refers to a historical Chinese, Japanese, Korean, Ryukyuan, and Vietnamese currency unit that was used as a superunit of the Chinese cash, Japanese mon, Korean mun, Ryukyuan mon, and Vietnamese văn currencies. The square hole in the middle of cash coins served to allow for them to be strung together in strings. The term would later also be used on banknotes and served there as a superunit of wén (文).

The mon was the currency of Japan from the Muromachi period in 1336 until the early Meiji period in 1870. It co-circulated with the new sen until 1891. Throughout Japanese history, there were many styles of currency of many shapes, styles, designs, sizes and materials, including gold, silver, bronze, etc. The kanji for mon (文) also shares its name with Chinese wén, Korean mun, Vietnamese văn.