The International Organization for Standardization (French: Organisation internationale de normalisation, Russian: Международная организация по стандартизации, tr. Myezhdunarodnaya organizatsiya po standartizatsii), widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial, and commercial standards. It has its headquarters in Geneva, Switzerland.

The three official languages of the ISO are English, French, and Russian. The organization's logos in two of its official languages, English and French, include the word ISO, and it is usually referred to by this short-form name. The organization says that ISO is not an acronym or initialism for the organization's full name in either official language; rather, recognizing that its initials would be different in different languages, it adopted ISO, based on the Greek word isos (ἴσος, meaning equal), as the universal short form of its name. However, one of the founding delegates, Willy Kuert, recollected the original naming question with the comment: "I recently read that the name ISO was chosen because 'iso' is a Greek term meaning 'equal'. There was no mention of that in London!"

An international organization is an organization with an international membership, scope, or presence. There are two main types: