BL Contains a hitherto untranslated paper by Einstein. The vacuum is fast emerging as the central structure of modern physics. How is this possible? What is the vacuum concept, and why is it so important? This collection brings together philosophically-minded specialists who engage these issues in the context of classical gravity, quantum electrodynamics, and the grand unification programme. The vacuum emerges as the synthesis of concepts of space, time, and matter; in the context of relativity and the quantum this new synthesis represents a structure of the most intricate and novel complexity. The Philosophy of Vacuum is unashamedly a project in metaphysics. The science of our time has transformed the concepts of space and time and of force and matter, yet the philosophy of Bohr and his school has found small purchase on the contemporary concerns of physics, and there are few guidelines to be found within the empiricist tradition of contemporary philosophy. However slippery the conundrums of metaphysical realism, the message of contemporary science remains the same: concepts and heuristics are grounded in consideration of what exists in the world. Here, then, is a work in modern metaphysics, in which the concepts of substance and space interweave in the most intangible of forms, the background and context of our physical experience: vacuum, void or nothingness.