Abstract: A hermetically sealable millimeter waveguide launch transition feedthrough for channelling high frequency electrical signals in a circuit which includes at least one waveguide. An aperture is formed in one wall of the waveguide and a conductive pin passes through the aperture. The pin is sealed therein by a dielectric material which surrounds the pin so as to isolate it from the waveguide wall. A probe head is disposed at one end of the conductive pin and within the waveguide. The opposite end of the pin contains a second probe head or other circuit connector. The transition may be effectively implemented in waveguide-to-waveguide or waveguide-to-device applications as well as in colinear device housing applications.