Cast iron, which usually refers to an in situ composite of stable eutectic graphite in a steel matrix, includes the major classifications of gray iron, ductile iron, compacted graphite iron, malleable iron, and white iron. This article discusses melting, pouring, desulfurization, inoculation, alloying, and melt treatment of these major ferrous alloys as well as carbon and alloy steels. It explains the principles of solidification by describing the iron-carbon phase diagram, and provides a pictorial presentation of the basic microstructures and processing steps for cast irons.