The phenomenon of CP violation—the breaking of the combination of charge-conjugation symmetry (C) and parity symmetry (P)—is one of the least understood aspects of high-energy physics. The first evidence for CP violation was reported in 1964 by a group led by Christenson et al. after studying neutral-kaon decays. It was later recognized in 1967 by Sakharov that CP violation is an important ingredient for resolving the mystery of why our Universe is dominated by matter over antimatter if they were created in equal quantities by the Big Bang. The quest for understanding CP violation has since drawn a great deal of attention from both the particle physics and cosmology communities. In 1973 Kobayashi and Maskawa showed that CP violation would emerge naturally in the presence of three families of quarks, establishing its mechanism in the standard model (SM) of particle physics.