In 1234 the first books known to have been printed in metallic type set were published in Goryeo Dynasty Korea. They form a set of ritual books, Sangjeong Gogeum Yemun, compiled by Choe Yun-ui. While these books have not survived, the oldest book existing in the world printed in metallic movable types is Jikji, printed in Korea in 1377. The Asian Reading Room of the Library of Congress in Washington, D.C. displays examples of this metal type. Commenting on the invention of metallic types by Koreans, French scholar Henri-Jean Martin described this as "remely similar] to Gutenberg's". However, Korean movable metal type printing differed from European printing in the materials used for the type, punch, matrix, mould and in method of making an impression.
A "Confucian prohibition on the commercialization of printing" also obstructed the proliferation of movable type, restricting the distribution of books produced using the new method to the government. The technique was restricted to use by the royal foundry for official state publications only, where the focus was on reprinting Chinese classics lost in 1126 when Korea's libraries and palaces had perished in a conflict between dynasties.