His autobiography is subtitled "Unterhändler der Menschlichkeit" ("Negotiator of humanity"). This is a reference to the leading role he played as a negotiator during Germany's division between 1949 and 1989 into two separate and at times mutually antagonistic states. Based in West Germany, he was part of a movement on the part of the protestant churches in West Germany to maintain contacts and provide support for in East Germany, where the ruling party was ubiquitous and officially hostile to religions other than Communism. It was in connection with the church contacts that he was able to maintain across the Inner German border that Geißel became involved in the controversial and originally secret Trading of East German political prisoners ("Häftlingsfreikauf") programme that operated between 1962 and 1989.