A rotary valve internal combustion engine has a piston connected to a crankshaft and reciprocatable in a cylinder, a combustion chamber being defined in part by the piston, and a rotary valve rotatable in a valve housing fixed relative to the cylinder, the rotary valve having a valve body containing a volume defining, in part, the combustion chamber and further having a port giving, during rotation of the valve, fluid communication successively to and from the combustion chamber via inlet and exhaust ports.