By 1973, the theoretical foundations of the Standard Model of fundamental interactions had been completed. In the decades that followed, new particles and phenomena predicted by the Standard Model were discovered in a dramatic series of experiments at laboratories around the world. This began with the discovery of the charm quark at SLAC and Brookhaven, predicted by Glashow, Illiopoulos and Maiani from flavor properties of the SM. The W and Z bosons were produced directly in experiments at CERN, and signals of energetic gluons were observed at DESY. Experiments eventually found a full third generation of fermions, culminating with the discovery of the top quark and tau neutrino at Fermilab. During this same period, major theoretical advances made it possible to push the accuracy of Standard Model predictions. This allowed compelling tests of the SM at the level of radiative corrections, and to test the predictions of QCD in the confining domain. Thus experiments confirmed the quantum dynamics of the SM, and validated the CKM picture of flavor mixing and CP violation. While this process took a long time, and may have appeared frustrating to many to just achieve the confirmation of the 'standard' theory, the outcome of these 30-odd years is now a cornerstone of our understanding of the natural world, occupying a deserved place next to Maxwell's electromagnetism, to relativity, and to quantum mechanics. The timescale and size of this enterprise, at the same time, gives us a benchmark for the magnitude of the efforts that may be required to go beyond the Standard Model to the next level of fundamental understanding. New ideas and theories have been put forward in the attempt to understand great questions left unanswered by the Standard Model. These theories attempt to explain why nature needs both gravitational and gauge interactions, and why their energy scales are so different. They address the possible origins of matter-antimatter asymmetry, of particle masses, and why there are three families of fermions. A major theme of these new ideas is unification, beginning with grand unified theories and the introduction of supersymmetry. The continued elaboration of these ideas was accompanied and by the development of string theory, and by the introduction of the see-saw mechanism for neutrino masses, linking their smallness with the natural scale of grand unification. A second major theme has been the attempt to understand electroweak symmetry breaking at Terascale energies, involving both supersymmetry and frameworks with new forces, large extra-dimensions, and even theories with no higgs boson. While none of these new ideas has yet been confirmed, increasing evidence has built up that the SM itself cannot account for everything we observe. The discovery of neutrino masses, the matter antimatter asymmetry of the universe, and dark matter are in fact physics Beyond the Standard Model. The need to extend the SM is more than a purely theoretical exigency; it has become a compelling empirical requirement. Plausible and calculable BSM scenarios, merging the pragmatic need to explain recent discoveries with the desire to answer the theoretically inspired great questions, guide the setting of directions for the future of particle physics.
