This collection includes the papers that laid the foundations of spacetime H. A. Lorentz, Michelson's Interference Experiment; H. A. Lorentz, Electromagnetic Phenomena in a System Moving with any Velocity Smaller than that of Light; H. 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 Bodies; A. Einstein, Does the Inertia of a Body Depend Upon its Energy Content? H. Minkowski, Space and Time; A. Einstein, On the Influence of Gravitation on the Propagation of Light; A. Einstein, The Foundation of the General Theory of Relativity; A. Einstein, Cosmological Considerations on the General Theory of Relativity; W. de Sitter, On the Curvature of Space; A. A. Friedmann, On the Curvature of Space; G. Lemaître, Expansion of the Universe, A Homogeneous Universe of Constant Mass and Increasing Radius Accounting for the Radial Velocity of Extra-Galactic Nebulæ. The texts are typeset in LaTeX.