This volume is a comprehensive and up-to-date compendium of worldwide experimental programs dedicated to the pursuit of atomic mass measurements. A tutorial section includes the various fields of physics in which atomic masses play an important role: nuclear physics, quantum electrodynamics, stellar nucleosynthesis, and weak interaction studies. There is a section devoted to theoretical approaches for both atomic and nuclear interactions, as well as a host of new projects for further advancing the field. This volume presents both an introduction and review of the current state of the art concerning mass measurements, evaluation, and prediction, and is suitable for graduate students and researchers in the field. No other volume is so devoted to the question of the atomic mass.