<p>The formation of magmatic sulfide deposits (MSDs) has been relatively well constrained over the past half century using traditional geochemical and isotopic techniques (e.g., Sr-Nd-Hf-Os-S). Despite this, questions remain regarding the nature of the mantle sources that fed world-class deposits, notably the importance of metasomatic changes to the generation of metal-rich melts. Addressing these fundamental questions may be accomplished, however, using novel metal isotope systems, such as Cu, Fe, Mg, Mo, and Zn. The strength of these isotope systems stems from the fact that they are independent of age, are largely unaffected by partial melting and fractional crystallization, exhibit lithophile, siderophile, and chalcophile affinities, and exhibit distinct signatures in geological reservoirs (e.g., continental crust, altered oceanic crust, subduction fluids). To date, only Cu, Fe, and, to a lesser extent, Mg have been applied to address the formation of MSDs. These isotope systems have provided a wealth of information on the metasomatic processes that modified mantle sources to MSDs (Cu, Fe, Mg), the sources of metals (Cu), the extent of metal enrichment (Cu, Fe), the importance of redox processes to deposit formation (Cu, Fe), and the evolution of sulfide liquids (Fe). Despite having not been directly applied to MSDs, Mo and Zn isotopes have a demonstrated potential to trace metasomatic processes in the mantle and distinguish metasomatic agents (e.g., subduction zone fluids, carbonatite melts, eclogite). Molybdenum and Zn isotopes may, therefore, broaden our current understanding of the potential importance of different styles of metasomatism to the formation of world-class MSDs.</p>