The Gesellschaft für Informatik e.V. (GI) (German Informatics Society) is one of two major societies for information technology professionals in Germany. The other one is the German Chapter of the ACM.
GI is organized in a number of Sections (Fachbereiche) (http://www.gi-ev.de/wissenschaft/fachbereiche/) which are divided into Committees (Fachausschüsse). Committees consist of a number of Special Interest Groups (Fachgruppen). Committees and Special Interest Groups may also have Working Groups (Arbeitskreise).
Of particular interest to HCI professionals is Fachbereich Mensch-Computer-Interaktion (FB MCI) (Section on Human-Computer-Interaction).