This study, compiled from lecture notes delivered over many years in the Mechanical Engineering departments of Istanbul Technical University and Işık University, presents the fundamental laws and definitions of thermodynamics through a systematic 12-week educational plan. Catering primarily to mechanical engineering but also to other engineering disciplines, the work serves as an international standard technical resource with equivalent content prepared in both Turkish and English. To develop students’ analytical skills, problems are included at the end of each lesson, supported by B.G. Kyle’s reference tables and enriched with answer keys. Combining theoretical depth with a pedagogical approach, this book is a reliable reference guide for both academic education and basic engineering applications.