This book is an informal introduction to the turbulence of fluids. The emphasis is placed on turbulence as a physical phenomenon. It addresses the unresolved issues, misconceptions, controversies, and major problems of the turbulence of fluids rather than the conventional formalistic elements and models. Little use is made of complicated formalisms; instead the emphasis is placed on an essentially informal qualitative form. The scope of the book is focused on the purely basic aspects of the turbulent flows of incompressible fluids. This book will certainly be of interest and use to graduate students as well as scientists active in fields where the turbulence of fluids is of importance. The book is intentionally written to appeal to a broad readership with the aim of making the turbulence of fluids interesting and comprehensible to the interested engineer.