This open access book is written by world-recognized experts in the fields of applied superconductivity and superconducting accelerator magnet technologies. It provides a contemporary review and assessment of the experience in research and development of high-field accelerator dipole magnets based on Nb₃Sn superconductor over the past five decades. The reader attains clear insight into the development and the main properties of Nb₃Sn composite superconducting wires and Rutherford cables, and details of accelerator dipole designs, technologies and performance. Special attention is given to innovative features of the developed Nb₃Sn magnets. The book concludes with a discussion of accelerator magnet needs for future circular colliders.