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The Sumitomo Clan 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. Riemon Soga, Masatomo Sumitomo's brother-in-law, learned Western methods of copper refining. In 1590 he established a smelting business named Izumiya, literally meaning "spring shop". The advanced techniques, which Riemon perfected, allowed the extraction of silver from copper ore, something which Japanese technology had as yet been unable to accomplish.
The smelting and smithing business, which was begun in Kyoto, was moved to Osaka by the late 17th century. 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 to export copper, import silk, and provide financial services. By 1691 copper mining had been added to the portfolio.
The Meiji Restoration allowed Sumitomo to import and utilize Western machines and techniques in its mines. Sumitomo soon branched out into even more business areas entering the machine and coal industries, as well as the forestry, banking and warehousing businesses becoming a zaibatsu, or business conglomerate.
In 1940s after World War II, almost all clan including the Sumitomo Clan were dissolved by GHQ & Japanese government.
As a result, although there are many companies still using a common word "Sumitomo" in their corporate names, the companies are managed independently listed on Tokyo and other stock exchanges with highly dispersed shareholders. Therefore, there are no relationships among the companies using Sumitomo's name (the companies are not in one group).
The companies using Sumitomo’s name together with KDDI signed an agreement with State owned Myanma Posts and Telecommunications (MPT) in July 2014 to jointly operate a mobile phone service in Burma for the next 10 years. 
Companies using Sumitomo's name
The Companies Using Sumitomo's name which are in the Nikkei 225
- NEC Corporation
- Sumitomo Chemical
- Sumitomo Corporation
- Sumitomo Electric Industries
- Sumitomo Heavy Industries
- Sumitomo Metal Industries
- Sumitomo Metal Mining Co., Ltd.
- Sumitomo Mitsui Financial Group
- Sumitomo Mitsui Trust Holdings
- Sumitomo Osaka Cement
- Sumitomo Realty & Development Co., Ltd.
- Company History Sumitomo Electric
- Sumitomo in History, part I: A Business Spirit Alive and Well After 400 Years, A Meeting with Copper Sumitomo Official Site
- Sumitomo Group, Encyclopædia Britannica article britannica.com
- Sumitomo in History, part II: Japanese Copper Across the Sea, Contributing to the Wealth of the Nation Sumitomo Official Site
- Sumitomo in History, part III: Japan's Kitchen, New Businesses Emerge Sumitomo Official Site
- About Us Sumitomo Corporation Official Site
- Sumitomo in History, part IV: Milestones, Major Copper Vein Discovered Sumitomo Official Site
- Sumitomo in History, part VI: A Time of Adversity, The End of Rule by the Samurai Sumitomo Official Site
- "KDDI, Sumitomo ink deal with Myanmar telecom for mobile phone service (17 July 2014)". http://english.kyodonews.jp. Kyodo News. Retrieved 17 July 2014. External link in
- "KDDI, Sumitomo ink deal with Myanmar telecom for mobile phone service". http://www.japantimes.co.jp. The Japan Times. Retrieved 17 July 2014. External link in
- "Corporate History - Sumisho Computer Systems Corporation". Scs.co.jp. Retrieved 2010-09-19.
- (English) Sumitomo Group Public Affairs Committee
- (English) Company profile and the origins of Sumitomo Official Sumitomo Site