In August/September 1999, a group of 68 physicists from 48 laboratories in 17 countries met in Erice, Italy, to participate in the 37th Course of the International School of Subnuclear Physics. This volume constitutes the proceedings of that meeting. It focuses on the basic unity of fundamental physics at both the theoretical and the experimental level. Contents: The Glorious Days of Physics (Dedicated to Bjo rn H Wiik) (K Johnsen, H Wenninger & G Wolf); Opening Lecture (G 't Hooft); Mini-courses on Basics (Z Kunszt, A Masiero, E W Kolb, B Greene & E Rabinovici); Experimental Highlights (K Nish