British engineering and construction company, founded in 1865 by Richard Costain and Richard Kneen, delivering transport, energy, water and defence infrastructure.

Costain Group plc traces its origins to 1865, when Richard Costain and his future brother-in-law Richard Kneen left the Isle of Man for Liverpool as jobbing builders. It is headquartered in Maidenhead and works across transport, energy, water and defence, from design and engineering through construction, commissioning and long-term asset management, with historic projects including the Dolphin Square apartments in London (completed 1937) and Dubai International Airport (completed 1960). Alex Vaughan is chief executive.