Heavy electrons are found among a number of lanthanide and actinide compounds, and are characterized by a large effective mass which becomes comparable to the mass of a muon. Heavy electrons exhibit rich phenomena such as unconventional superconductivity, weak antiferromagnetism and pseudo metamagnetism, however, many of the established ideas and techniques relating to theoretical and experimental physics of strongly correlated electrons are insufficient to understand heavy electrons. On the theoretical side, enormous amounts of quantum fluctuations have brought disaster to celebrated...