This book marks the centenary of the discovery of the electron by J.J. Thomson in 1897, one of the great turning points in the history of scientific ideas. In this book the discussion moves from the historical context of the discovery of the electron and its basic properties, to the Dirac equation, bonding in condensed matter, Fermi and non-Fermi liquids, quantum order, superconductivity, heavy, coherent and composite electrons, and the role of the electron in the cosmos, with each chapter being written by a leading figure in the field.