The transmission of waves along a straight cylindrical conductor is discussed and an analysis made of the method of launching by means of a conical horn. It is shown that the efficiency of launching depends on the horn angle and aperture and that the launching loss is probably due to the generation of complementary waves which dissipate their energy as heat in the conductor. Details are given of experiments on a surface-wave transmission line at a wavelength of 6.5 cm, and suggestions are made for reducing the launching loss.