Abstract: An intake and exhaust valve system (10) for an internal combustion engine having a combustion chamber (19) within a cylinder (13) closed at one end by a cylinder head (17). A cavity (25) is provided in the cylinder head opening onto the combustion chamber through a first port (27). The valve system (10) has first and second valves one of which is an intake valve (31) movable between open and closed conditions for controlling intake fluid flow into the combustion chamber (19) and the other of which is an exhaust valve (33) movable between open and closed conditions for controlling exhaust gas flow from the combustion chamber. The first valve (31) comprises a valve head (35) sealingly engagable with the first port (27) and a skirt structure (31).