This book collects the Proceedings of the Workshop "Incontri di Fisica delle Alte Energie (IFAE) 2006, Pavia, 19-21 Aprile 2006." The workshop is the fifth edition of a series of workshops on fundamental research in particle physics, as carried on at the most important international laboratories, and possible fallouts in medical and technological applications. Researches in this field aim at identifying the most elementary constituents of matter.