Molybdenum, found naturally as molybdenite, is converted through MoO
3
to compounds in a wide range of oxidation states, coordination numbers, and states of aggregation. The diverse chemistry of molybdenum is manifest in a wide array of uses in biological and industrial systems. Molybdenum, an essential component of many enzymes, plays a primary role in nitrogen fixation and nitrate reduction in bacteria and plants, and sulfite and xanthine oxidation for microorganisms, plants, and animals. Industrially, molybdenum compounds are important in lubrication, where the disulfide and oil‐soluble molybdenum sulfur complexes serve as antifriction and antiwear agents; in hydrodesulfurization and hydrotreating of petroleum; ammoxidation and other catalytic processes; in anticorrosion formulations; as flame and smoke retardants; and in a variety of coatings and pigments. Biomedically, molybdenum is used in nuclear medicine and is under study in a number or therapeutic procedures. The trioxide, several molybdates, and the disulfide are available as bulk chemicals.