An internal combustion engine comprises a four stroke working cylinder, a four stroke EGR cylinder, an intake system for supplying a combustion air charge to the cylinders, a first exhaust system for removing exhaust gas from the four stroke working cylinder and to the atmosphere and a second exhaust system for removing exhaust from the four stroke EGR cylinder and to the intake system, wherein the combustion air charge is a combination of combustion air and exhaust gas from the four stroke EGR cylinder.