The Goportis Consortium consists of the three German National Subject Libraries. One key area of collaboration is digital preservation. The Goportis Digital Archive is jointly used by the consortial partners. As part of their quality management the partners strive to obtain certifications for trustworthy digital repositories. The Goportis Consortium successfully applied for the Data Seal of Approval (DSA) and is currently working on the application for the nestor Seal. The poster illustrates the collaboration of the Goportis partners during the certification process (distribution of tasks, time frame, etc.). This way it could serve as best-practice example.