Metal casting is an important manufacturing technology for efficiently producing massive components with complex shape. A large share of industrial castings is made from iron and steel alloys, combining attractive properties and low production cost. Upgrading of properties in cast iron and steel is mainly achieved by alloying and in fewer cases by heat treatment. Molybdenum is an important alloying element in that respect, increasing strength, hardness and toughness. It also facilitates particular heat treatments such as austempering. The paper describes the metallurgical functionality of molybdenum alloying in iron-based castings and demonstrates its effectiveness for applications in the automotive and mining industry.