Between the fourteenth and the eighteenth centuries, there was created under the Yi Dynasty in Korea a remarkable series of astronomical instruments, star-charts and clocks. The present volume is the result of close collaboration between four distinguished historians of Asian science to demonstrate the context, purpose, nature and specific workings of these early scientific instruments. Specially commissioned drawings and other illustrations demonstrate their complexities of design and operation. A brief introduction is given to the Chinese background of Korean astronomy and astronomical instrument-making and to the renaissance of Korean astronomy in the early fifteenth century. In a detailed examination of the instruments made under the supervision of King Sejong in the 1430s, there is documentation of the re-equipping of the Royal Observatory, with identification of the individual instruments involved. A survey of the succeeding two centuries gives the background to Song Iyong’s instrument, identified as a demonstrational armillary sphere in the Koryo University Museum.