The internship program in Korea began in April 1914 with 6 interns working at Severance Hospital. The direct reason for implementing the internship program was to protect graduates of Severance Union Medical School who did not yet have a medical license. In the late 1910s, the internship program stabilized. Intern applicants were required to have a medical license to enter the internship program, and the subjects that interns studied and the training period became stricter. Above all, Severance Hospital had allocated a budget for interns every year since 1918. The reason why the internship program was institutionalized in just a few years was that the interests of both interns and Severance Hospital were aligned. Interns were able to acquire the qualifications and clinical skills of general physicians by experiencing each department of clinical medicine for one year. Based on various clinical experiences, the interns prepared to open their private practice. Meanwhile, Severance Hospital was able to reduce the burden on full-time medical staff while operating the hospital 24 hours a day by using low-paying interns. Around 1930, the internship program expanded. A dual system of interns and externs and a system of assigning senior interns also appeared. In addition, starting in the 1930s, the number of interns always exceeded 10. As we have seen above, the internship program was a system required by both the intern applicants and hospital, and was also a training system suitable for modern society. This was why the internship program continued in various medical institutions after liberation or during the Korean War.