Magnetic crystals are ideal systems to study the universal properties of phase transitions, particularly systems with quenched randomness and frustration. Pure systems with different symmetries provide the foundation for studies in corresponding systems with quenched randomness. Because phenomena near phase transitions have universal properties, results from bulk magnetic crystals provide a basis for understanding phase transitions in films and nanoparticles, as well as many non-magnetic materials. This motivates the subject of this book, which discusses phase transitions studies in magnetic crystals from the perspective of an experimentalist who has done extensive work in the field. The advantage is that many experimental techniques are described in sufficient detail for a good understanding of the results and their comparison to theory.