The book is the result of the Italian conference on General Relativity, held in Italy in September 1998. One of the main features of this conference has been to bring together mathematicians and physicists, experts in different fields: General Relativity, Variational and Topological methods, Differential Geometry, Astrophysics. Classical and Quantum aspects of General Relativity have been debated and various new results have been presented. Perspectives on the search of Gravitational waves have been illustrated. These methods permit to study the geodesical connectedness of space-times and to relate to topological properties to the multiplicity of the geodesics joining two given events. Critical point Morse theory has been used to study light rays on Lorentzian manifolds and to interpret the gravitational lensing effect.