Abstract: An apparatus for dielectric welding has an opposed pair of relatively movable electrodes (14, 12), each incorporating an electrically conducting element with a working surface close to and opposed to that of the other electrode. There is a gap (15) between the electrodes, such that a material to be welded may be placed in the gap and may be pressed between the electrodes, and radio frequency signals are supplied (16, 18) to the electrodes. At least one of the electrodes (14) incorporates a layer (14b) of dielectric material covering the conducting element (14a) both on the working surface and on surfaces which are alongside the working surface, so that the dielectric material (14b) defines at least part of the gap (15). The thickness covering the working surface is significantly less than that covering the alongside surfaces.