This volume, the proceedings of the Coral Gables Conference, held December 12-16, 2000, contains some recent developments in the theory of gravitation, and discusses, in particular, the fact that gravity, like electrodynamics, is both attractive and repulsive. This property of gravitation enables us: (1) to explain the observed expansion of the universe, and, at the same time, its increasing acceleration; (2) to clarify the reasons for the expansion of the universe, together with competing forces of repulsive quintessence and the gravitational force of ordinary matter. Furthermore, given very strong gravitational forces of black holes, particles reach high energies and copiously emit gamma rays as well as neutrinos. The fact that these gamma rays burst at cosmic regions does imply that gravity can be a source of electromagnetism. We have thus obtained an experimental fact that the two long-range forces of gravity and electricity are unified. The conference also had discussions on neutrino masses, the cosmological constant, and violation of the Lorentz invariance.