This book reviews the concept of mass as it is defined, interpreted, and applied in contemporary physics and critically examined in the modern philosophy of science. It focuses on theories proposed after the mid-1950s, covering recent experimental and theoretical investigations into the nature of mass and its role in modern physics.

The book begins with the difficulties of defining inertial mass in a non-circular manner and discusses the question of whether mass is an observational or a theoretical concept. It then studies the notion of mass in special relativity and gives a critical analysis of the different derivations of the famous mass-energy relationship E = mc² and its conflicting interpretations. The book concludes with a presentation of recently proposed global and local dynamical theories of the origin and nature of mass.