Middle Korean language in the context of Mongol invasions of Korea

Goryeo (Korean: 고려; Hanja: 高麗; MR: Koryŏ; pronounced [ko.ɾjʌ]; Middle Korean: 고ᇢ롕〮, romanized: kwòwlyéy) was a Korean state founded in 918, during a time of national division called the Later Three Kingdoms period, that unified and ruled the Korean Peninsula until the establishment of Joseon in 1392. Goryeo achieved what has been called a "true national unification" by Korean historians as it not only unified the Later Three Kingdoms but also incorporated much of the ruling class of the northern kingdom of Balhae, who had origins in Goguryeo of the earlier Three Kingdoms of Korea. According to Korean historians, it was during the Goryeo period that the individual identities of Goguryeo, Baekje and Silla were successfully merged into a single entity that became the basis of the modern-day Korean identity. The name "Korea" is derived from the name of Goryeo, also romanized as Koryŏ, which was first used in the early 5th century by Goguryeo; Goryeo was a successor state to Later Goguryeo and Goguryeo.

Goryeo was established in 918 when general Wang Kŏn, after rising under the erratic Taebong ruler Kung Ye, was chosen by fellow generals to replace him and restore stability. Throughout its existence, Goryeo, alongside Unified Silla, was known to be the "Golden Age of Buddhism" in Korea. As the state religion, Buddhism achieved its highest level of influence in Korean history, with 70 temples in the capital alone in the 11th century. Commerce flourished in Goryeo, with merchants coming from as far as the Middle East. The capital in modern-day Kaesong, North Korea was a center of trade and industry. Goryeo was a period of great achievements in Korean art and culture.

The mun (Korean: 문; Hanja: 文, Late Middle Chinese: 文, romanized: mjun, Middle Korean: 문, romanized: mwun) was introduced as the main currency of Korea in 1625 and stayed in use until 1892. Prior to the mun, cash coins with the inscriptions tongbo (通寶) and jungbo (重寶) and silver vases called ŭnbyŏng were used as currency in the Goryeo Dynasty (918–1392), as well as imported Chinese currency. The mun resembled and was derived from the Chinese wén (cognate also to the Japanese mon, Ryukyuan mon, and the Vietnamese văn). Coins denominated in mun were cast in copper-alloys such as brass or bronze and were round with square holes. From the 17th century until the end of the 19th century, coins denominated in mun bearing the inscription Sangpyeong Tongbo (상평통보, 常平通寶), introduced in 1633, were the most widely circulated currency. In 1888, coins were struck in small numbers denominated in mun and won (written as "warn", which were equal to 1000 mun). The mun was replaced in 1892 when the yang was introduced.

The cast coins of the mun would remain in circulation long after their abolition. They continued to be legal tender in Korea at a value of 0.1 chon (1⁄1000 won) until 1908, when they were revalued to 0.2 chon, or 1⁄500 won.