This book deals with a new class of magnetic materials, spin ice. Spin ice has become the canonical example of modern frustrated magnetism where competing interactions between spins set the rules for an emergent magnetostatic gauge field theory. Excitations take the form of magnetic monopoles or can condense via a Higgs mechanism. Beyond classical spin ice, the book describes the new physics emerging when quantum coherence (spin liquids, photon-like excitations) and itinerant electrons (anomalous Hall effect) are included in artificial systems. This first book dedicated to spin ice is a review of the current understanding of the field, both on the theoretical and experimental levels, written by leading experts. The book is written in a linear way with very few prerequisites. It also contains textbook-like descriptions of theoretical methods to help advanced students and researchers to enter the field.