In 1967 a group of physicists from the University of Bologna, led by A Zichichi, published a proposal to search for a heavy lepton using the Frascati (e+e-) collider. The proposal, whose key pages are reproduced in this book on the 30th anniversary of the publication, was the consequence of many years of work started at CERN, where, in addition to the original idea of searching for a heavy lepton carrying its own leptonic number, new technologies were invented to allow the detection of a signal whose identification against the high background of hadronic processes was extremely difficult.More than ten years of work by A Zichichi, together with his students and his collaborators, have paved the way for the discovery of the Third Family of fundamental particles. In this authoritative volume, a group of eminent physicists unequivocally establishes the origin of the Third Family of the basic constituents of matter.