The Molybdenum Supplement Volume B/7 covers binary molybdenum sulfides and sulfide ions, the most prominent being molybdenum sulfide MoS2 on account of its numerous practical applications. It is a dry lubricant material and has become indispensable in high-vacuum and space applications. Semiconducting MoS2 photoelectrodes have achieved sizable solar energy conversions in photoelectrochemical cells. Its capability to reversibly intercalate lithium ions enables the construction of low-weight, high efficiency, secondary batteries. MoS2 doped with cobalt is useful as a catalyst of the hydrosulfurization of organic compounds. All these remarkable properties are related to its layered structure built up of covalently bound SMoS sheets held together by only weak van der Waals forces.