This textbook provides a strong foundation in the basic thermodynamics needed to analyze real-world engineering applications of thermodynamics in the field of energy systems. Written in a format readable to students new to the subject, this book will also help entrepreneurs venturing into the world of energy and power without a background in mechanical engineering. This book presents the basic theories of thermodynamics by focusing on the application of the subject matter to the most common applications of thermodynamics. It takes real-world problems from the author's over 40 years of experience as a practical, professional engineer and provides in-depth solutions to each problem using concepts the student has learned from earlier chapters. The case studies provide both examples of how thermodynamics is used in state-of-the-art tools to solve the case studies' problems, as well as ideas for future energy-efficient systems.