The Standard Model of particle physics is extremely successful in describing nature. It is, however, incomplete in one major way: the masses of gauge bosons and fermions enter the Standard Model through the Higgs mechanism. That is completely satisfactory technically, but it is not understood physically. We do not yet know what nature really does to give mass to particles. Understanding Higgs physics is necessary in order to complete the Standard Model, and to learn how to extend it and improve its foundations.This book is a collection of current work and thinking about these questions by...