This collection (typeset in LaTeX) includes the papers that laid the foundations of spacetime physics: H. A. Lorentz, Michelson's Interference ExperimentH. A. Lorentz, Electromagnetic Phenomena in a System Moving with any Velocity Smaller than that of LightH. Poincaré, Sur la dynamique de l'électron (5 June 1905)H. Poincaré, Sur la dynamique de l'électron (23 July 1905)A. Einstein, On the Electrodynamics of Moving BodiesEinstein, Does the Inertia of a Body Depend Upon its Energy Content?H. Minkowski, The Fundamental Equations for Electromagnetic Processes in Moving BodiesH. Minkowski, Space and TimeA. Einstein, On the Influence of Gravitation on the Propagation of LightA. Einstein, The Foundation of the General Theory of RelativityA. Einstein, Cosmological Considerations on the General Theory of RelativityW. de Sitter, On the Curvature of SpaceA. A. Friedmann, On the Curvature of SpaceG. Lemaître, A Homogeneous Universe of Constant Mass and Increasing Radius Accounting for the Radial Velocity of Extra-Galactic Nebul