This book has been written as a textbook for students seeking a professional degree in agricultural engineering. The authors believe that for students with this objective the course of study should be primarily analytical, rather than descriptive, and that the analytical approach should apply t only to ideas but also to quantitative procedures and computations. We recognize that sound analysis, particularly in applied fields, is based on the understanding of theoretical principles and on kwledge of many practical considerations. We have tried to maintain a good balance between the preparation of theory and practice, but we favor emphasis of theoretical considerations on the basis that they usually are t mastered except in an organized course of study, whereas practical kwledge is more easily assimilated. To present both theory and practice makes heavy demands on class time and textbook space. For this reason it has been possible to treat in detail only a few typical environmental systems for livestock housing and storing agricultural products as a means of illustrating methods of analysis and the application of principles. It is presumed, however, that such study will prepare the student for work with other types of structures.