Town affiliations linking cities in the United States with ones in other countries made their appearance shortly after World War II, and became known as "Sister Cities." In 1956, the practice became a national effort when President Eisenhower proposed the "People-to-People" idea at a White House conference, having as its objective the involvement of people and organized groups at all levels of our society in "personal diplomacy." His hope was to increase and strengthen understandings across international lines, with the objective of promoting world peace.

In the first few years of the program, only a dozen or so active affiliations were started- including Stockton's affiliation with Shimizu. During the 1960's, however, the number of city affiliations began to increase rapidly, and it became clear that a national organization devoted exclusively to the support of the Sister City idea was needed. In response, the "Town Affiliation Association" was officially incorporated in June, 1967 as "membership organization to foster better international understanding and cooperation through Sister City Relationships."

Sister Cities International (SCI), of which Stockton Sister Cities Association is a member, has evolved as the principle program of the Town Affiliation Association, and is the organization through which Sister City activity in the United States is promoted and coordinated. Currently, SCI represents 2,3975 U.S. Cities, counties, and states and their 1,137 partners in 137 countries worldwide. There are 3,305 cities around the world (1,283 U.S. and 2,022 international) that are involved in U.S. international sister city programs. Combined, they account for 2,191 affiliations and pairings.

Recognized Sister City relationships can be established only by the concurrent actions of the official governing bodies of the cities involved. Prospective relationships may be suggested by private citizens, private groups, or public officials within a community, or by an invitation from a city elsewhere in the world, but until both cities officially agree, it remains just that, "a suggestion."

Stockton's program - one of the oldest in the United States, having been inaugurated in 1959, less than three years after the White House conference - has come to encompass relationships with six cities in as many countries: since 1959, with Shimizu in Japan; since 1964, with Iloilo City in the Philippines; since 1973, with Empalme, in Mexico; since 1993, with Foshan in China; since 1998, with Parma, in Italy; since 2005, with Battambang, in Cambodia; and since 2006, with Asaba, in Nigeria.