This new book includes important papers written by R. Cahill, J. G. Hartnett, F. Cardone, A. Marrani and R. Mignani, J. Dunning-Davies, A. Gutierrez-Rodriguez, M. A. Hernandez-Ruiz and J. M. Rivera-Juarez, A. Vankov, P. O'Donell, J. Lopez-Bonilla et al, V. Varlamov, G.-j. Ni. Interesting mathematical questions of relativity theory, relations to the modern astrophysics, as well as some conceptual foundations are considered in the papers.