OneBeacon Insurance Group, Ltd. is a Bermuda-domiciled holding company that is publicly traded on the New York Stock Exchange under the symbol "OB". OneBeacon Insurance Group's underwriting companies offer a range of specialty insurance products sold through select independent agents, regional and national brokers, and wholesalers. The company's businesses include OneBeacon Professional Insurance, International Marine Underwriters, Entertainment Brokers International Insurance Services, Specialty Accident and Health, OneBeacon Government Risks, OneBeacon Energy Group, A.W.G. Dewar (tuition refund), collector cars and boats written through Hagerty Insurance Agency, OneBeacon Technology Insurance, OneBeacon Financial Services, OneBeacon Specialty Property, Property and Inland Marine, OneBeacon Excess and Surplus Lines, and AutoOne.

As one of the oldest property and casualty insurers in the United States, OneBeacon traces its roots to 1831 and the Potomac Fire Insurance Company. Today, OneBeacon's specialty insurance businesses are national in scope.