In the past 20 years, energy density functional (EDF) approaches have become a powerful framework to study the structure and reactions of atomic nuclei. This book provides an updated presentation of non-relativistic and covariant energy functionals, single- and multi-reference methods, and techniques to describe small- and large-amplitude collective motion or nuclei at high excitation energy. Detailed derivations, practical approaches, examples and figures are used throughout the book to g...