Waehaksŏ refers to Japanese language study books compiled by those related to the Sayŏgwon, a foreign language study institution in the Chosŏn Dynasty. Korean language research on Japanese-related sources has focused on the Waehaksŏ, especially the large volume of conversational texts in the Chŏphae Sinŏ. Since the late 1990s, Korean language study books and records remaining in Japan have been discovered and reported to the academia, and since the 2000s, late modern Korean-Japanese language study books have also begun to be the subject of research. However, full-scale Korean language research is still insufficient. Therefore, from the perspective of “Korean language historical materials related to Japan,” it is necessary to conduct Korean language research not only on Japanese studies books from the Chosŏn period, but also on late modern Korean-Japanese language study books and Korean language-related records. In addition, while increasing the accessibility of related sources, translations and annotations of important sources such as Chŏphae Sinŏ will be made in order to increase the depth of the research. Meanwhile, as has been attempted recently, interdisciplinary research in various fields such as language education, literature, cultural history, and social history should be actively conducted using sources containing Korean language historical materials related to Japan. For this purpose, close collaboration with not only Japanese language majors but also with majors in various fields is essential.