These proceedings of a workshop held at Isle-aux-Coudres, Quebec, Canada in August 1993, provide a comprehensive, up-to- date assessment of a fundamental subject in modern stellar astrophysics. Hot, luminous stars play a crucial role in the rapid recycling of matter in dense regions of the Universe. The most luminous objects generate the strongest outflows of material, which in turn have a profound impact on both the interstellar medium and the underlying stars themselves. However, recent observational and theoretical advances have shown that these outflows are highly unstable and inhomogeneous. These characteristics constitute a fundamental property of the outflows that can no longer be disregarded. Instability and Variability of Hot-Star Winds provides an in-depth assessment of this important phenomenon from both an observational and a theoretical perspective. It includes up-to- date discussions of the observational diagnostics of time- dependent stellar-wind structure, the theoretical understanding of the origin of such structures, and its consequences for the process of mass loss via stellar winds. The book presents some 40 invited papers, each followed by in-depth discussions which occupied nearly half of the workshop schedule. A round-table discussion summarizes the current state of affairs. This book is suitable for researchers and graduate students studying the radiation hydrodynamics of hot-star winds and related areas of research (e.g. astrophysical flows, turbulence).