There used to be a saying in mathematical circles that went something like "Children work with equalities; grownups work with inequalities. " An overstatement perhaps, but a facility with inequalities does seem to be necessary for an understanding of much of mathematics at intermediate and higher levels. In particular, a working knowledge of inequalities can be beneficial to the practicing engineer. Inequalities are central to the definitions of all limiting processes, including differention and integration. When exact solutions are unavailable, inconvenient, or unnecessary, inqualities can be used to obtain error bounds for numerical approximation. Inqualities can also lead to an understanding of the qualitative behavior of solutions. This guide to inequalities was written specifically with engineers and other applied scientists in mind. It is intended to help fill the gap between college-algebra level treatments of inqualities that everyone has seen before, and the formidable treatise on the subject that exist in the mathematics literature. Every chapter ends with a rich collection of exercises. The book should be accessible to senior-level engineering students, graduate students, and practicing engineers.