The study of the rise and fall of great mathematical ideas is undoubtedly one of the most fascinating branches of the history of science. It enables one to come into contact with and to participate in the world of ideas. Nowhere can we see more concretely the enormous spiritual energy which, initially still lacking clear contours, begs to be moulded and developed by mathematicians, than in Riemann (1826-1866). He perceived mathematics and physics as one discipline and thought of himself as both mathematician and physicist. His ideas as well as their contemporary descendants are the theme of this book. Audience: This volume will be useful to those interested in such diverse fields as the mathematics of physics, algebra and number theory, topology and geometry, analysis, and the history of science.