In 1950, the first ideas for cooperation between Wiesbaden and Mainz on an economic and local political level were put into concrete terms. The initiators initially met informally before the Rhine-Main special-purpose association founded in 1939 was revived in 1954 for cooperation in the economic and cultural fields. Disputes over responsibilities and the still unresolved question of the affiliation of the AKK suburbs finally led to the founding of the Mainz-Wiesbaden Cities Committee in November 1958 as a separate body for cooperation between the two cities.

Since 1959, members of the municipal councils, the city councils and representatives of the offices involved as well as the Lord Mayors have been exchanging views in the joint Cities Committee.

The agreement on the joint use of the Wiesbaden abattoir in 1967, the purchase of a joint fireboat and the founding of the Mainz-Wiesbaden transport association in 1974 were major successes.

In October 1969, the neighbourhood agreement between the two state capitals came into force and simplified mutual economic and organizational relations. Within the framework of this agreement, the Mainz-Wiesbaden Cities Committee acts as a mediator in the event of differences between the specialist departments, businesses, companies or other institutions of the contracting parties. Other topics include energy supply, the future of local public transport, school issues and the development of commercial areas.