The mechanism of cross-link formation in sulfur vulcanization mediated by bis(dimethyldithiocarbamato)zinc(II), ZDMC, has been uncovered, utilizing a combination of Density-Functional calculations and model experiments. These studies have revealed that, in a three-stage process, ZDMC exhibits a unique combination of catalytic activity: (1) It mediates the reaction between sulfur and rubber. This is achieved by incorporating sulfur atoms in the zinc-dithiocarbamate ring and inducing their insertion into an allylic C-H bond via an ene-like reaction. This ene reaction yields a rubber-bound polythiothiol and is only slightly endothermic, even though an activation energy of similar to 90 kJ mol(-1) is required. (2) The resulting polythiothiols engage in equilibrated metathesis reactions to yield polysulfides, the initial sulfur cross-links. (3) In a hitherto unsuspected mechanistic step ZDMC has been found to shift the metathesis equilibrium to the side of crosslinks by mediating desulfhydration of the polythiothiols, producing sulfides and H2S. Thus, the combined results of theoretical and experimental work have allowed to put forward a novel mechanism for ZDMC-mediated sulfur cross-link formation that successively comprises (a) homogeneous catalysis of thiol formation from sulfur and rubber, (b) an equilibrium between polythiothiol intermediates and cross-links and (c) ZDMC-induced desulfhydration.