The Muon Anomalous Magnetic Moment: Standard Model Theory and Beyond

QED, Hadronic, and Electroweak Standard Model contributions to the muon anomalous magnetic moment, a_mu = (g_mu-2)/2, are reviewed. Theoretical uncertainties in the prediction a_mu^SM = 116591597(67) times 10^{-11} are scrutinized. Effects due to ``New Physics'' are described. Implications of the current experiment vs. theory constraint a_mu^exp - a_mu^SM = 453(465) times 10^{-11} and anticipated near term error reduction to +- 155 times 10^{-11} are discussed