This monograph on fluid mechanics is not only a superb and unique textbook but also an impressive piece of research. The author writes from the vantage point of a mathematical physicist: Having in mind the important applications and approximation techniques used in physics and engineering, he carefully analyses the power of the theory. He examines, among others, the theories of Leray, Ruelle and Takens, and discusses Lorenz's ideas of attractors. This is the only textbook that fully covers turbulence, all the way from the works of Kolmogorov to modern dynamics. This 2nd corrected printing has been thoroughly revised with many changes to improve readability.