Geophysics, the science of the agencies which modify the earth, requires by nature an international cooperative system of investigation. For this reason, the period from 1882 to 1883 was designated as the IPY, during which scientists from 11 countries joined for the first time in an investigation of the meteorological phenomena, magnetic field, and polar lights in the high northern latitudes. 50 years after the first international observation of the earth were carried out, a second such investigation was conducted over a period ranging from 1932 to 1933, this time scientists from 44 countries participated in an investigation that included the ionosphere in its scope. The observations were not limited to the high latitudes, but other important parts of the earth, as well. The world-wide interest in this approach of cooperative study of the earth was further hightened in the third international investigation conducted 25 years later, from July 1, 1957 to the end of 1958. During this 18-month period, the observations were made at some 4000 stations scattered around the entire surface of the earth, with about 20,000 scientists from 66 countries participating in them. Since 1960 when the Republic of Korea became a member of the International Union of Geodesy and Geophysics, a scientific organization under the control of the International Council of Scientific Unions, our geophysicists and the related organzations have been actively engaged in research work, exchanging information with other scientists of the world.