There is no doubt that Albert Einstein has been one of the most brilliant minds of the past century. His major contribution to science was the special and the general theory of relativity, which gave a new dimension to that we call today "Modern Physics". Many people feel frustrated because when they try to understand relativity, they find some authors that expound in their books a complex arrangement of equations referring to the mathematical part of the theory, namely, the books are accessible for people with certain levels of knowledge (that is the case of engineers, physicists, mathematicians, among others). Nevertheless, perceiving and anticipating this situation, Albert Einstein wrote this book (more than fifty years ago) whit the purpose of exposing the special and the general theory of relativity in such a way that anyone can understand it. I this sense, I think, Einstein succeeded because despite the shortness of the book, the same covers the most important aspects of relativity in a clear and concise form. Moreover, the book has appendixes where the author makes reference to some interesting subjects like the problem of space and relativity, the experimental confirmation of the theory, to name a few. If you have decided to learn something about relativity, and you do not have vast knowledge in physics and mathematics, I sincerely recommend you this book. On the other hand, if you were a reader looking for more technical information (mathematical foundation of general relativity), I would choose the book "Gravitation" written by Misner, Wheeler y Thorne. This text represents an encyclopedia about general relativity.