Abstract: This chapter aims to provide a broad historical overview of the major developments in General Relativity Theory (‘GR’) after the theory had been developed in its final form. It will not relate the well-documented story of the discovery of the theory by Albert Einstein, but rather will consider the spectacular growth of the subject as it developed into a mainstream branch of physics, high-energy astrophysics, and cosmology. Literally hundreds of exact solutions of the full non-linear field equations are now known, despite their complexity [1]. The most important ones are the Schwarzschild and Kerr solutions, determining the geometry of the solar system and of black holes (Section 1.2), and the Friedmann–Lemaître– Robertson–Walker solutions, which are basic to cosmology (Section 1.4). Perturbations of these solutions make them the key to astrophysical applications.