Ductile iron, also known as nodular iron or spheroidal graphite iron, is second to gray iron in the amount of casting produced. This article discusses the common grades of ductile iron that differ primarily by the matrix structure that contains the spherical graphite. The grades of ductile iron designated by their tensile properties in the specification ASTM A536 are presented in a table. The article various reviews factors, such as microstructure, composition, and section effect, affecting the mechanical properties of ductile iron. It discusses the hardness properties, tensile properties, shear and torsional properties, damping capacity, compressive properties, fatigue properties, and fracture toughness of ductile iron. The article concludes with information on the applications of austempered ductile iron.