Twin towns and sister cities are two of many terms used to describe the cooperative agreements between towns, cities, and even counties in geographically and politically distinct areas to promote cultural and commercial ties.

In the United Kingdom, the term twin towns is most commonly used, generally referring to town-twinning with Europe, differentiating with the term sister cities, which is used for agreements with towns and cities in the Americas. In Europe, a variety of terms are used; most commonly twin towns, but partnership towns, partner towns and friendship towns, are also used. Germany and Poland use Partnerstadt(Ger.) / Miasto Partnerskie (Pol.) (Partner Town/City), France uses Ville Jumelée (Twinned Town/City), while Italy has gemellaggio (twinning) and comune gemellato (twinned municipality). In the Netherlands, the term Stedenband (City bond) is used. North America, South America, South Asia, Australasia and Asia generally use the term sister cities. In the former Soviet Block countries twin towns is used, as well as the term brother cities.