While presenting current knowledge as well as unsolved problems in our understanding of the sun, this book also shows the fascinating interplay between particle physics and astrophysics -- culminating in the discovery of neutrino oscillations. The text begins with an overview of how the model of the sun and thus of stars in general evolved over time, a development accompanied and maintained by some of the greatest discoveries in physics, ranging from the evolution of quantum mechanics, via nuclear physics right up to modern questions in particle physics. Special emphasis is placed on the current generation of solar neutrino observatories, and although neutrino oscillations form the central subject of the book, open questions and problems as well as possible solutions are also discussed.