This book describes the memorable theoretical work that motivated the construction of the electron-positron accelerators at CERN and SLAC, and the monumental experimental effort that led to a verification of the main theoretical expectations at these laboratories and at Fermilab.The aim is to provide a description of the theoretical work, as well as a synthesis of the experimental effort, which makes interesting reading for both theorists and experimentalists. In particular, the experimental measurements, discussed in the second part of the book, are systematically related to the theoretical...