Thermal analyses and optimizations are very ubiquitous and important in academic research and engineering applications. In this field, the entropy generation minimization has been widely used and found to be effective in many cases. Sometimes, it was even used without checking the applicability, and seemed to be a unified theory that could solve all thermal problems. Is this really the case? This book answers this question through detailed theoretical derivations and different numerical examples in heat transfer and heat-work conversion. It shows clearly that the theory has limitations and a definite application scope, beyond which it may provide unreasonable or incorrect results. Therefore, the entropy generation minimization is far from perfect. This book will be of interest to students, researchers and engineers in thermal science and engineering, as it will help the reader to apply the entropy generation minimization correctly.