This graduate-level text extends beyond mathematical derivations to elaborate on physical ideas underlying relativity, with a historical introduction and examinations of special theory (space-time transformations, four-dimensional formulations, mechanics, optics, electromagnetism), and general theory (space-time continuum, gravitation, experiments, and relativistic cosmology). Contents: Historical Introduction. Part 1 - The Special Theory: 1. Space-Time Transformations. 2. Four-Dimensional Formulation of the Theory. 3. Mechanics. 4. Optics. 5. Electromagnetism. Part 2 - The General Theory: 6. General Transformations in the Space-Time Continuum. 7. Geometrization of Gravitation. 8. Experimental Tests of Einstein's Theory of Gravitation. 9. Relativistic Cosmology. Appendices - Differential Geometry of a Curved Surface. 1974 edition.