It has been argued that the provision and organization of In-Service Education and Training (INSET) for teachers in Korea has been carried out under the strong leadership of government authorities. However, it was not until the early 1970s that laws and government institutes specifically for INSET provision were established and began to fulfill the function that they have today. This study investigates the historical context and development of INSET in Korea prior to the formation of the current system, with a particular focus on the major actors and their respective roles. The findings indicate that there existed a variety of private organizations which provided INSET for teachers, ranging from research institutes, voluntary groups, and universities to overseas educational commissions. Their participation not only contributed to diversifying the contents of the training, but could also stand in for the government in the areas in which its influence was not yet fully extended.