ISO 3166-1, as part of the ISO 3166 standard, provides codes for the names of countries and dependent territories, and is published by the International Organization for Standardization (ISO). The official name of the standard is Codes for the representation of names of countries and their subdivisions – Part 1: Country codes. It defines three sets of country codes:

• ISO 3166-1 alpha-2, a two-letter system, used in many applications, most prominently for country code top-level domains (ccTLDs), with some exceptions.
• ISO 3166-1 alpha-3, a three-letter system, which allows a better visual association between country name and code element than the alpha-2 code.
• ISO 3166-1 numeric, a three-digit numerical system, with the advantage of script (writing system) independence, and hence useful for people or systems which uses a non-Latin script. This is identical to codes defined by the United Nations Statistics Division. ISO 3166 has included alphabetical country codes since its first edition in 1974, and numeric country codes since its second edition in 1981. The country codes were first published as ISO 3166-1 in 1997 in the fifth edition of ISO 3166, when ISO 3166 were divided into three separate parts.

ISO 3166-1 is not the only standard for country codes. Many international organizations use their own country codes, where some of them closely correspond to the ISO 3166-1 codes.