Penguin decays of B mesons

Penguin, or loop, decays of B mesons induce effective flavor-changing neutr al currents, which are forbidden at tree level in the standard model. These decays give special insight into the CKM matrix and are sensitive to non-s tandard-model effects. In this review, we give a historical and theoretical introduction to penguins and a description of the various types of penguin processes: electromagnetic, electroweak, and gluonic. We review the experi mental searches for penguin de cays, including the measurements of the elec tromagnetic penguins b --> s gamma and B --> K*gamma and gluonic penguins B --> K pi, B+ --> omega K+ and B --> eta'K, and their implications for the standard model and new physics. We conclude by exploring the future prospec ts for penguin physics.