A discovery that neutrinos are not the usual Dirac but Majorana fermions, i.e. identical to their antiparticles, would be a manifestation of new physics with profound implications for particle physics and cosmology. Majorana neutrinos would generate neutrinoless double-$beta$ ($0 ubetabeta$) decay, a matter-creating process without the balancing emission of antimatter. So far, 0$ ubetabeta$ decay has eluded detection. The GERDA collaboration searches for the $0 ubetabeta$ decay of $^{76}$Ge by operating bare germanium detectors in an active liquid argon shield. With a total exposure of 82.4 kg$cdot$yr, we observe no signal and derive a lower half-life limit of T$_{1/2}$ > 0.9$cdot$10$^{26}$ yr (90% C.L.). Our T$_{1/2}$ sensitivity assuming no signal is 1.1$cdot$10$^{26}$ yr. Combining the latter with those from other $0{ u}betabeta$ decay searches yields a sensitivity to the effective Majorana neutrino mass of 0.07 - 0.16 eV, with corresponding sensitivities to the absolute mass scale in $beta$ decay of 0.15 - 0.44 eV, and to the cosmological relevant sum of neutrino masses of 0.46 - 1.3 eV.
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