The Arbeitsgemeinschaft deutschsprachiger Planetarien (ADP) is a non-formal workshop of staff members at any planetarium as well as contributors in popular astronomy. The ADP was founded by Prof. Hans-Ulrich Keller during the inauguration of the new planetarium building in Stuttgart on April 22nd, 1977. It was agreed upon an annual conference of the directors and their collaborators. It has grown to an open forum for people interested in planetariums. The ADP benefits from the exchange of information in the German speaking region. It is an important platform for discussions on technical, methodical and didactical issues linked to planetaria. This includes the presentation of new advancements which are exhibited by international vendors and producers of planetarium technology. Sometimes, space agencies and research facilities participate. An appointed regular date turned out to be the second week-end after Easter.