The vast majority of particles in particle physics are today considered to be bound states of other particles. All forms of binding energy and kinetic energy in such a state have to be included in its inertial mass. This book revives the classical explanation for this in the case of electromagnetic interactions. But it is also a reminder of the many benefits of this classical understanding that are simply dropped in modern accounts of inertia. This is a book for the motivated student who feels it is useful to remember where our theories come from. There is also a comprehensive overview of the state of the art in particle physics.