This book presents the fundamental principles of thermodynamics and heat transfer, providing a solid foundation for understanding energy systems. From the core concepts of basic thermodynamic state parameters and ideal gases to the complexities of real gases and vapors, this book provides the knowledge to analyze and manipulate energy in various engineering applications. It covers topics such as heat capacity, thermodynamic processes, and the First Law of Thermodynamics, giving insights into how energy is harnessed and utilized. The book explores advanced subjects like second law thermodynamics, circular cycles, and the thermodynamic analysis of thermal power cycle installations, unveiling the intricacies of energy efficiency. The second section of the book shifts focus to heat transfer mechanisms, covering thermal conductivity, convective heat transfer, and thermal radiation. The book is useful to anyone interested in the complexities of energy dynamics in engineering systems.