Cooperation, interchange or intertrade of complementary currencies is not yet very common, perhaps of because the funding impulse of most complementary currencies does not cover the question of interchange and cooperation yet, or because theoretical aspects are not often studied. The article describes money or currency as an instrument of cooperation, based on a sociological and institutional economics background. It then postulates currency as an operating system and focuses on the technical terms of trade if one would try to establish cooperation between such systems. Basic principles of interchange and intertrade, which are necessary for success, are presented, such as the ideas of trade balance, compensation funds, exchange rates and clearing, set-points and limits, references, anchoring money and tolls and taxes. Further some aspects of governance and negotiation are discussed and a nested framework of rules is adapted to currencies. As an Appendix a case study of the Zurich region is presented where a process of negotiation and building of an interchange network between several CC-groups is on-going.