The International Atomic Energy Agency (IAEA) was established in 1957. It is an international organization in which the peaceful use of nuclear energy for the benefit of mankind - in keeping with the spirit of the times - was implemented as the central focus of its work. It is not surprising that the USA and the USSR were among the founding members, along with Hungary, Indonesia, the UK, Egypt and Brazil. However, the fact that the Vatican was also a founding member of this international body may seem surprising at first glance. On closer inspection, however, this clearly visible entry into the international sphere of diplomatic efforts seems more than understandable: The Holy See wanted to see the international stage as a diplomatic space of opportunity and as a theological and political space of discourse. The theological perspective with which the Holy See appeared - in the form of the visibly active Secretariat of State - suggested an emerging theological constant of papal diplomacy, dynamized and turned towards the international community as the context of ecclesiastical action. The "preservation of creation", as a theological option without alternative, was recognized by all actors as a vital and decisive guiding principle for diplomatic action in the contemporary "world of today". The IAEA was one of the first international organizations in which the Vatican wanted to participate conceptually. The proposed lecture aims to present these processes, to work out their conceptual-theological implications and to analyze the perspectives and developments that result from them.