Sumitomo Group (住友グループ, Sumitomo Gurūpu^?) is one of the largest keiretsu, founded by Masatomo Sumitomo.

The Sumitomo group traces its roots to a bookshop in Kyoto founded circa 1615 by a former buddhist priest, Masatomo Sumitomo. Considered its spiritual founder, even today management of the group is guided by his "Founder's Precepts", written in the 17th century.

It was copper that made the company famous, however. When Riemon Soga, Masatomo Sumitomo's brother-in-law, learned purportedly Western methods of copper refining, he established a smelting business in 1590. This he named Izumiya, literally meaning "spring shop". The advanced techniques Riemon perfected allowed extraction of silver from copper ore, something which Japanese technology had as yet been unable to accomplish.

While the smelting & smithing business began in Kyoto, by the late 17th century it was moved to Osaka, and Soga passed control of the company to his son Tomomochi who managed its transformation into a major trading house during the Edo period. Sumitomo began exporting copper, importing silk, providing financial services, and by 1691 copper mining had been added as a business, too.