  Spin physics had its beginnings in the famous experiments of Stern and
Gerlach, which eventually resulted in the postulation of spin by Goudsmit and
Uhlenbeck. The Stern-Gerlach experiment told us that the $g$-value of the
electron was 2, but we now know that because of radiative corrections, the
$g$-value of the leptons is slightly greater than 2, the lowest-order
contribution being $\alpha/\pi$, where $\alpha$ is the fine-structure constant.
Measurements of the magnetic dipole moments of the electron and muon have
played a major role in our understanding of QED and of the standard model. In
this talk I discuss the progress on measurements and theory of the magnetic
dipole moment of the muon.
