Using fundamental physics, the theory of stellar structure and evolution is able to predict how stars are born, how their complex internal structure changes, what nuclear fuel they burn, and their ultimate fate. This undergraduate textbook provides a clear, methodical introduction to the theory of stellar structure and evolution. Starting from general principles and axioms, step-by-step coverage leads students to a global, comprehensive understanding of the subject. Throughout, the book uniquely places emphasis on the basic physical principles governing stellar structure and evolution. All processes are explained in clear and simple terms with all the necessary mathematics included. Exercises and their full solutions allow students to test their understanding. This book requires only a basic background in physics and mathematics and assumes no prior knowledge of astronomy. It provides a stimulating introduction for undergraduates in astronomy, physics, planetary science and applied mathematics taking a course on the physics of stars.