This is an advanced textbook on the subject of turbulence, and is suitable for engineers, geophysicists, and applied mathematicians. The aim of the book is to bridge the gap between the elementary, heuristic accounts of turbulence to be found in undergraduate texts, and the more rigorous, if daunting, accounts given in the many monographs on the subject. Throughout, the book combines the maximum of physical insight with the minimum of mathematical detail.