This text presents papers given at a discussion meeting of The Royal Society, held in July 1992, concerning thin film diamond. Traditionally, commercial diamond synthesis was almost entirely by the high-pressure, high-temperature technique, but in recent years, low-pressure diamond synthesis has attracted world-wide interest due to the possible use of diamond films in commercial applications. These papers review these low-pressure diamond synthesis techniques. An historical overview of the low-pressure growth techniques and a description of diamond and crystal morphology is given, followed by a discussion of the kinetics and gas phase chemistry involved in thin film growth. Peter Bachmann presents a review of the current deposition techniques, and summarizes the results of various deposition conditions to show that diamond growth is only possible in a narrow range of gas compositions. Other chapters discuss the electronic, optical, thermal and mechanical properties of thin diamond films as well as the electronic structure, deposition techniques and applications of diamond-like carbon (DLC) films. The final chapter discusses the various thermal and optical infra-red and X-ray applications of diamond thin films. Researchers in materials, physics and mechanical engineering should find this text a timely review of a rapidly advancing field, and it should provide practising engineers in the electronic and manufacturing industries with a useful overview of the field.