Since the hydrogen laser near 160 nm was reported in 1970, there has been dramatic progress in the development of sources of coherent light in the vacuum ultra-violet (V.U.V.). This review will discuss recent experimental work and relevant basic physical principles of V.U.V. lasers. It is a consequence of the requirement for high-power excitation that high-current relativistic electron beams have been utilized most successfully for pumping V.U.V. lasers. Thus there is a significant interest in elucidating the kinetic details of the formation and decay of the excited species from which laser action has been observed. The hydrogen, carbon monoxide and noble gas molecular dissociation lasers are described in terms of the experimental configurations employed and their kinetic spectroscopy. The maximum power levels reported are ≥102 kW cm-2 in Lyman band of hydrogen(6), 4·8 kW cm-2 in the Werner band of deuterium(11), at 90 K, 15 W cm-2 in carbon monoxide(27) and 60 MW cm-2 in xenon(39). Details of the recently developed high-power, tunable xenon laser(61) are also presented. An account of coherent radiation in the V.U.V. obtained through harmonic generation is included as an integral part of the future potential of V.U.V. spectroscopy. It is hoped that this review will stimulate further investigation of the photophysical properties of present and future laser systems excited by ionizing radiation. © 1975.