Sister cities or twin towns are local school and/or chamber of commerce programs designed to foster international communication and cooperation. Like the city version of a "pen pal", a city is assigned one or more similarly sized and situated international cities. Sisters cities usually share characterstics, such as both being coastal cities or island-cities. The programs include exchange students or economic programs.
The Sister Cities program was begun in 1956 by Dwight Eisenhower. It was originally administered as part of the National League of Cities, but since 1967 has been a separate organization: Sister Cities International.