  A summary is given of the present status of the theory and experiment of the
anomalous magnetic moment of the muon. A difference between predicted and
measured values is an indication of physics beyond the Standard Model. A new
experimental number has produced a value which differs from a recent Standard
Model prediction by about 1.6 standard deviations. When the new result was
first announced, the discrepancy was about 2.6 standard deviations, but
theorists have recently found an error in the sign of the largest term in the
Standard Model hadronic light-by-light contribution which reduces the
difference. Additional data are being analyzed and elements of the theory are
being scrutinized to provide, in the future, a sharper test of theory.
