Goethe thought that prefaces were useless, and I am not disposed to disagree. Yet there may be value in stating, somewhere between the covers of this book, that its purpose is to present the basic principles of mechanics of fluids and to illustrate them by application to a variety of problems in different branches of engineering. Emphasis, however, is on principles rather than engineering practice. Attention is also given to the assumptions on which the principles rest, for only thus can the limits of their validity be appreciated. Although the book is intended primarily for students taking honours degrees in engineering, it should also serve the needs of those studying for the CEI examinations in Fluid and PartieIe Mechanics. It is a book for engineers rat her than mathematicians. Stress is laid on physical concepts rather than mathematics; specialized mathematical techniques are avoided and algebraic manipulations are kept to aminimum. For the majority of students, the occasional small sacrifice of rigour is, I believe, more thanjustified by the greater ease of visualizing and understanding the physical circumstances. The book is reasonably self-contained, but references are given to more detailed discussions of certain topics. These references are not intended as an exhaustive bibliography but rather as useful eIues to start the search for further information.