An internal combustion engine including at least one cylinder with a piston moveable therein in an engine block in which microwaves are introduced into a combustion chamber through a microwave window, wherein the combustion chamber is formed by a piston base and a cylinder head, characterized in that the combustion chamber includes a combustion chamber wall which functions as a microwave window at least in portions wherein the combustion chamber wall is made from a wall layer that is made from a ceramic material in which wall layer at least one annular circumferential hollow conductor cavity is arranged with at least one inlet opening for the microwave and which includes at least one outlet opening for the microwave that is run in the annular hollow conductor cavity of the wall layer. In general the invention provides safe ignition of lean fuel air mixtures.