Fundamental interactions are mediated by bosonic fields, quanta of which are realized as particles. The properties of these fields typically obey certain symmetry rules. In this book we discuss the symmetry between two types of interactions — electromagnetic, which are familiar to anyone who turned on the electric lights, and weak, which govern the nuclear reactions that fuel the Sun. While there is a symmetry between these two types of interactions, it is broken. The unified theory of electroweak interactions was developed over 50 years ago. The Higgs scalar field named after one of the theorists that proposed it, is believed to be responsible for the breaking of the electroweak symmetry. Yet, it is only now after the discovery of the Higgs boson in 2012 by the LHC experiments, that we can study the mechanism of the electroweak symmetry breaking. This book discusses the theoretical developments that led to the construction of this theory, the discovery and the experimental observations that need to come to fully establish the validity of the model.