The aim of this book is threefold. Firstly, we intended to give a text-book on Relativity Theory and on Einstein’s Theory of Gravitation. Secondly, we wanted to give an exposition of our own researches on these subjects. Thirdly, our aim was to develop a new, non-local, point of view on the theory and to correct a widespread misinterpretation of the Einsteinian Gravitation Theory as some kind of general relativity.