This volume contains the lectures presented at the NATO Advanced Study Institute on "Frontiers of Laser Spectroscopy of Gases" held in the Hotel Golf Mar, Vimeiro, near Torres Vedras, Portugal from 30 March to 10 April 1987. The objective of the meeting was to take stock of the recent technological developments involving lasers and to assess their impact on spectroscopy. The whole range of wavelengths from the far infrared through to the extreme ultraviolet was covered. In addition, specific applications to both atoms and molecules were described. Indeed, one of the most successful and pleasant aspects of the Institute was the joint participation of atomic physicists and molecular spectro- scopists, who meet all too rarely these days. The Institute also succeeded in covering a wide time span from the very earliest days of lasers to some of the very latest developments in both lasers and their applications to spectroscopy. There were 14 invited lecturers, giving a total of 40 lectures, and 89 other participants at the Institute. Each of the invited lecturers has contributed a chapter to this volume. In addition, on Thursday 2nd April a special one-day session was held in the Chemistry Department at the University of Coimbra to mark the retirement of Professor Dr. F.