Neutrinoless double beta-decay is the key process to gain understanding of the nature of neutrinos. The GErmanium Detector Array (GERDA) is designed to search for this decay of the isotope Ge-76. Germanium crystals enriched in Ge-76, acting as source and detector simultaneously, will be submerged directly into an ultra pure cooling medium that also serves as a radiation shield. This concept will allow for a reduction of the background by up to two orders of magnitudes with respect to earlier experiments.JRC.D.4-Isotope measurement