ISO 3166 is a standard published by the International Organization for Standardization (ISO). It defines codes for the names of countries, dependent territories, special areas of geographical interest, and their principal subdivisions (e.g., provinces or states). The official name of the standard is Codes for the representation of names of countries and their subdivisions. It consists of three parts:

The first edition of ISO 3166 was published in 1974, which included only alphabetic country codes. The second edition, published in 1981, also included numeric country codes, with the third and fourth editions published in 1988 and 1993 respectively. The fifth edition, published between 1997 and 1999, was expanded into three parts to include codes for subdivisions and former countries.

The ISO 3166 standard is maintained by the ISO 3166 Maintenance Agency (ISO 3166/MA), located at the ISO central office in Geneva, Switzerland. Originally it was located at the Deutsches Institut für Normung (DIN) in Berlin, Germany. Its principal tasks are: