Any student working with the celebrated Feynman Lectures will find a chapter in it with the intriguing title Electromagnetic Mass [2, Chap. 28]. In a way, it looks rather out of date, and it would be easy to skate over it, or even just skip it. And yet all bound state particles we know of today have electromagnetic mass. It is just that we approach the question differently. Today we have multiplets of mesons or baryons, and we have colour symmetry, and broken—avour symmetry, and we think about mass and energy through Hamiltonians. This book is an invitation to look at all these modern ideas with the help of an old light. Everything here is quite standard theory, in fact, classical electromagnetism for the main part. The reader would be expected to have encountered the theory of elec tromagnetism before, but there is a review of all the necessary results, and nothing sophisticated about the calculations. The reader could be any student of physics, or any physicist, but someone who wouldlike to know more about inertia, and the clas sical precursor of mass renormalisation in quantum field theory. In short, someone who feels it worthwhile to ask why F= ma.