This volume contains new publications of two important works that have never been published together and are two firsts: (i) A. S. Eddington's Report on the Relativity Theory of Gravitation (2ed, Fleetway Press, London 1920), which was the first systematic exposition of Einstein's general relativity, and (ii) the first experimental test of general relativity carried out by F. W. Dyson, A. S. Eddington and C. Davidson and reported in the paper "A Determination of the Deflection of Light by the Sun's Gravitational Field, from Observations Made at the Total Eclipse of May 29, 1919" (Phil. Trans. R. Soc. Lond. A 1920 220, pp. 291-333). The answer to the question "Why should Eddington's Report be reprinted again, given that there exist hundreds of excellent books on general relativity?" was given in 1983 by the renowned astrophysicist and recipient of the 1983 Nobel Prize for Physics S. Chandrasekhar: "Eddington's Report is written so clearly and yet so concisely that it can be read, even today, as a good introductory text by a beginning student."