Recently, I bought a number of cheap Dover textbooks on (mathematical) topics I am going to study coming semester, including Abstract Algebra, Differential Geometry and Functional Analysis. I found some of the books remarkably clear and well-written, but as I was reading through them and looked at the publication date I wondered whether the material was still relevant for my university studies. Of course, experts may say that great textbooks will always continue to be great textbooks, but my question concerns the link with present-day courses and research. How much value is there in studying old texts if one is mainly concerned with understanding the material so as to do well in university and later on? Also, how long does a textbook go along before the material becomes irrelevant? Would it still be worth looking through Soviet era textbooks from the 1950s?