Abstract: An ignition device for igniting a gaseous medium, such as a fuel/air mixture, comprises a chamber having a wall provided with an aperture through which the chamber can be placed in communication with the medium to be ignited, a first electrode extending across said chamber to said aperture to define an annular gap between the tip of said first electrode and the wall of said aperture, which wall forms at least part of a second electrode, and a third electrode surrounding and insulated from said first electrode and defining a second gap within said chamber between said third electrode and one of said first and second electrodes.