The role of thermodynamics in modern physics is not just to provide an approximate treatment of large thermal systems, but, more importantly, to provide an organising set of ideas. Thermodynamics: A complete undergraduate course presents thermodynamics as a self-contained and elegant set of ideas and methods. It unfolds thermodynamics for undergraduate students of physics, chemistry or engineering, beginning at first year level. The book introduces the necessary mathematical methods, assuming almost no prior knowledge, and explains concepts such as entropy and free energy at length, with many examples. This book aims to convey the style and power of thermodynamic reasoning, along with applications such as Joule-Kelvin expansion, the gas turbine, magnetic cooling, solids at high pressure, chemical equilibrium, radiative heat exchange and global warming, to name a few. It mentions but does not pursue statistical mechanics, in order to keep the logic clear.