Descemet membrane endothelial keratoplastyKeratoplasty (DMEKDMEK) has become the gold standard in Germany for the treatmentTreatment of corneal endothelial diseasesEndothelial disease; however, the widespread use of DMEKDMEK was initially limited due to problems with donor preparationDonor preparation and the difficulty of correctly and gently unfolding the endothelial Descemet membrane (EDM) in the anterior chamber. This chapter describes the appropriate donor selection followed by the safe donor preparationDonor preparation of the corneaCornea without tearing or even rupturing the EDM, including the indispensable peripheral semicircular orientation marking. Also presented is a step-by-step atraumatic loading of the glass cartridge, the introduction of the EDM roll into the anterior chamber, and its safe step-by-step unfolding based on (1) the sequential use of jets of fluid, (2) repeated tapping on the peripheral/central corneaCornea, (3) controlled flattening of the anterior chamber, (4) use of air bubbles of defined size and finally, the fixation of the EDM in correct orientation to the back of the host corneaCornea with a gas bubble. Since every wrong step with DMEKDMEK can have far-reaching consequences for patient and surgeon, this step-by-step pragmatic approach should minimize the incidence of donor tissue damage and failure in patient maneuversPatient maneuvers.