During the Koryŏ period (918–1392), the Korean peninsula witnessed vibrant merchant activity, foreign and domestic ones alike. Not only Chinese but also Central and West Asian merchants came to the peninsula, while Koryŏ merchants visited China-based dynasties and cultivated relationships with merchants from regions beyond China. In the first half of the dynasty, especially during the eleventh and twelfth centuries, Song merchants frequently visited Koryŏ, while Koryŏ merchants expanded their already thriving businesses in China. Then in the second half of the dynasty, especially in the fourteenth century, the Koryŏ merchants extended their activities to Central Asian as well as West Asian Islamic markets. Examination of the Koryŏ merchants and their trade with the outer world helps us understand how the Koryŏ people viewed the outside, and how Koryŏ in general dealt with their foreign counterparts in commercial terms.