What Is or What Might Be the Legacy of Felix Klein?

Felix Klein was an outstanding mathematician with an international reputation. He promoted many aspects of mathematics, e.g. practical applications and the relation between mathematics and natural sciences but also the theory of relativity, modern algebra, and didactics of mathematics. In this article about the The Legacy of Felix Klein we firstly refer to his ideas in university teaching of mathematics teacher students and the three books "Elementary Mathematics from a higher (advanced) standpoint" from the beginning of the last century. Secondly we refer to his interests in school mathematics and his influence to the "Merano Resolution" (1905) where he pleaded for basing mathematics education on the concept of function, an increased emphasis on analytic geometry and an introduction of calculus in secondary schools. And thirdly we especially discuss the meaning and the importance of Klein's ideas nowadays and in the future in an international, worldwide context.