|  | |
| Public K.K. | |
| Traded as | : | 
| Industry | Insurance | 
| Fate | Merged | 
| Successor | MS&AD Insurance Group | 
| Founded | October 21, 1918 (as Taishō Marine and Fire Insurance Co.) October 2001 (merger of Mitsui Marine & Fire Insurance Co. and The Sumitomo Marine & Fire Insurance) | 
| Headquarters | Tokyo, Japan | 
| Area served | Worldwide | 
| Key people | Yoshiaki Shin, Chairman Toshiaki Egashira, President | 
| Revenue |  JP¥ 2,137,603 million (FY 2007) | 
|  JP¥ 40,027 million (FY 2007) | |
| Number of employees | 20,237 (2008) | 
| Website | www.MSIG.com | 
Mitsui Sumitomo Insurance Group Holdings, Inc. (三井住友海上グループホールディングス株式会社 Mitsui Sumitomo Kaijō Gurūpu Hōrudingusu Kabushiki-Kaisha?) is a Japanese insurance holding company headquartered in Tokyo, Japan.
MSIG was formed in 2001 from the merger of Mitsui Marine & Fire Insurance Co. (itself descended from the Taishō Marine and Fire Insurance Co. founded in 1918) and The Sumitomo Marine & Fire Insurance. In 2010 April Aioi Insurance Co., Ltd., Nissay Dowa General Insurance Co., Ltd., merged into MSIG, making the group's name changed in to MS&AD Insurance Group Holdings, Inc.. According to this business integration, MS&AD has become the largest property insurance company in Japan, with market share of 33% in 2013.
On 8 September 2015, it was announced that Mitsui Sumitomo had agreed to buy the UK Insurance firm Amlin for £3.5bn