It used to be difficult to reliably fabricate clean heterostructures using magnetic and superconducting layers. Today this is no longer the case; such reproducible superconductor/ferromagnet heterostructures enable the quantitative study of the rich and varied phenomena associated with ferromagnet/superconductor proximity effects. These structures are eminent, suitable candidates for many switching devices, ranging from non-volatile low power memory elements to quantum computing applications involving Josephson junctions. This book's main purpose is to explain how the equilibrium and transport properties of these heterostructures can be accurately calculated starting from a standard BCS type Hamiltonian. The main techniques, including both analytical and numerical methods, are discussed in detail. Results obtained from these calculations are shown to be in excellent quantitative agreement with experiment. This is a theory book, but the theory is neither abstruse nor esoteric. Knowledge of only introductory graduate physics has been assumed; a solid undergraduate training and a bit of perseverance would also be enough. This book can easily be read and understood by experimentalists, and just about anybody can grasp the basics by referring to the figures and explanations. Quite apart from the manifold applications of superconductor/ferromagnet nanostructures, studying them provides us with considerable insights into fundamental physics and the general study of hybrid nanomaterials.