This student textbook has been designed for chemical and mechanical engineering departments with courses in fluid mechanics. The text makes extensive use of simple theories to predict and correlate fluid motions. Emphasis is placed on the development of skill in deriving theoretical solutions for problems by example and practice. As far as possible, the accuracy and range of applicability of the various theoretical models are evaluated by comparison with experimental data. The text stresses the identification or derivation of relevant models and conditions, rather than theory and mathematics. A set of problems have been provided for practice in such derivations.