"For over three decades@ open gearing for many applications has been successfully designed and manufactured from ductile iron. Examples spanning a full range of size and transmitted power are in service in various process industries throughout the world@ proving the soundness of this material selection in technical as well as economical terms. The latest metallurgical and manufacturing developments have re-established the practical limits for this material@ well beyond what was considered possible as recently as a few short years ago. A ductile iron gear of 16 m diameter@ 340 BHN (min.) hardness@ module 42@ with a face width of 1200 mm and having AGMA Q10 teeth quality@ capable of transmitting 2x10 000+ kW was previously a concept. Today@ such a gear can be manufactured. Despite its long and successful service history@ ductile iron remains a somewhat lesser known commodity as an open gearing material. The goal of this paper is to present the current ""state-of-the-art"" with respect to ductile iron as a gear material@ including its mechanical properties as applicable to gear design@ structural characteristics@ typical manufacturing and inspection plans@ and in-service behavior. For each of these aspects@ ductile iron will be compared to other available materials for open gearing design and manufacture@"