is one of the largest keiretsu in Japan and one of the largest corporate groups in the world.
The major companies of the group include Mitsui & Co. (general trading company), Sumitomo Mitsui Banking Corporation, Nippon Paper Industries, Pokka Sapporo Holdings, Toray Industries, Mitsui Chemicals, Isetan Mitsukoshi Holdings, Sumitomo Mitsui Trust Holdings, Mitsui Engineering & Shipbuilding, Mitsui O.S.K. Lines and Mitsui Fudosan.
Founded by Mitsui Takatoshi (1622–1694), who was the fourth son of a shopkeeper in Matsusaka, in what became Mie prefecture. From his shop, called Echigoya (越後屋), Mitsui Takatoshi's father originally sold miso and ran a pawn shop business. The family would later open a second shop in Edo (modern Tokyo).
Takatoshi moved to Edo when he was 14 years old, and later his older brother joined him. Sent back to Matsutaka by his brother, Takatoshi waited for 24 years until his older brother died before he could take over the family shop, Echigoya. He opened a new branch in 1673; a large gofukuya (kimono shop) in Nihonbashi, a district in the heart of Edo. The genesis of Mitsui's business was in the Enpō era, which was a nengō meaning "Prolonged Wealth".
In time, the gofukuya division separated from Mitsui, and became Mitsukoshi. Traditionally, gofukuyas provided products made to order; a visit was made to the customer's house (typically a person of high social class or who was successful in business), an order taken, then fulfilled. The system of accountancy was called "margin transaction". Mitsui changed this by producing products first, then selling them directly at his shop for cash. This was then an unfamiliar mode of operation in Japan. Even as the shop began providing dry goods to the government of the city of Edo, cash sales were not yet a widespread business practice.
Edo's government had struck a business deal with Osaka. Osaka would sell crops and other material to pay its land tax. The money was then sent to Edo—but moving money was dangerous in middle feudal Japan.