One of the lasting heritages of the International Geophysical Year (1957–58) is the system of world data centers (WDC) through which there has been international exchange of a wide variety of geophysical data on a continuing basis. This voluntary exchange mechanism has been remarkably successful. The basic operating costs of the centers are provided by the host country. The international exchanges are mainly by barter. The data providers number in the thousands and the users in the tens of thousands.