In the planning and implementation of the deep geothermal project in Trebur (Hesse), early public participation was central for the Überlandwerk Groß-Gerau GmbH. The Risk Dialogue Foundation designed a citizen participation process on the “if”, “where” and “how” of the ongoing project. Many questions were answered during seven public DialoGGeo citizens’ forums. Furthermore, the Geothermal Advisory Board, which accompanies the project, dealt with central issues and recorded them in a public final report in the form of broadly supported assessments and demands. Another important milestone was reached in 2015 with workshops for the specific needs of local residents. Through this multi-year participation process, it was possible to develop an intensive fair and early engagement with the project and to integrate the most diverse needs. To find a solution, the geothermal project as a whole was discontinued and reflected on in a final advisory board meeting.