Discovered in 1778, molybdenum occurs naturally in molybdenite (or molybdenum disulfide, MoS₂), an ore that is chiefly found in western U.S. and Canada and Chile.

Molybdenum is a hard, silver-white metal. It has the highest melting point (2610 ^oC) of any metal except tungsten and tantalum and has strong thermal and electical conductivity.

"Moly steel" is an important technological advance brought about by modern warfare. During World War II, the German army constructed a giant piece of artillery that can be moved about on a railroad car. The Allies called the gun "Big Bertha", and discovered that the steel included the use of molybdenum - a metal that previously had no practical application. Adding molybdenum in steel imparts toughness for heavy service, and in heat-resistant alloys. With these properties, "moly steel" is used in boiler plate, rifle barrels and filaments. No vessel could be found to cast it until a special water-cooled crucible was devised in 1959.

In the early 1980s, a company, Moli Energy Ltd, was established in Burnaby, British Columbia to manufacture a rechargeable lithium battery using molybdenite as the cathode material and lithium as the anode. This rechargeable battery was superior to the nickel-cadmium rechargeable battery. But the reactivity of the lithium electrode was a major safety concern.

Other compounds of molybdenum have applications in grease lubricants and pigments and as catalysts. Molybdenum is necessary in trace amounts in plant nutrition and is also valuable in human metabolism.