This book presents a collection of research papers, written by physicists, philosophers and historians of science who had participated in the Zentrum fur interdisziplinare Forschung (ZiF) during the academic year 1992/93 in order to discuss the nature and structure of spacetime as it is used in general relativity. All contributions focus on unsolved questions, such as the possibility of time machines, referential indeterminacy, the hole problem, and the conventional vs. empirical character of spacetime. These papers having a more historical colour deal with Einstein's view of general covariance and with the epistemological status of space(time) in the works of Carnap, Weyl and Hilbert, all of whom relate their position to Husserl's phenomenology, yet in fundamentally different ways.