The recent discovery of a dark companion object orbiting the star VB8 has transformed our knowledge and understanding of low-mass stellar companions. This book reviews present observational and theoretical knowledge of Brown Dwarfs. These objects bridge the range of masses between conventional planets and normal stars. The book is based on papers presented at a recent workshop, held at George Mason University, and devoted to Brown Dwarfs, Fourteen papers are concerned with various search techniques and the results so far; a further dozen contributions consider the theoretical aspects. As an aid to the reader, there are excellent indexes which enable any mention of a particular celestial object to be located quickly. It is anticipated that sub-stellar mass objects will be directly detectable with the Hubble Space Telescope. This survey volume is therefore a timely summary of our knowledge prior to the launch of the telescope.