In this introductory textbook, Principles of Thermodynamics, Jean-Philippe Ansermet presents thermodynamics as a natural extension of mechanics. The book begins with the foundational principles of thermodynamics, using concepts from mechanics to introduce readers to the theory. In the second part, a broad spectrum of applications is covered, which are crucial in physics, chemistry, and engineering, such as calorimetry, phase transitions, heat engines, and chemical reactions. The final section delves into continuous media, deriving Fourier and Fick’s laws, diffusion equations, and various transport phenomena using a unified approach. Each chapter ends with worked examples and exercises to reinforce key concepts, and a full solutions manual containing over 150 problems is provided at the end of the book, addressing contemporary issues faced by scientists and engineers for both undergraduate and graduate students.