  A comprehensive theory of the Lamb shift in light muonic atoms such as
$\mu$H, $\mu$D, $\mu^3$He$^+$, and $\mu^4$He$^+$ is presented, with all quantum
electrodynamic corrections included at the precision level constrained by the
uncertainty of nuclear structure effects. This analysis can be used in the
global adjustment of fundamental constants and in the determination of nuclear
charge radii. Further improvements in the understanding of electromagnetic
interactions of light nuclei will allow for a promising test of fundamental
interactions by comparison with ``normal" atomic spectroscopy, in particular,
with H-D and $^3$He-$^4$He isotope shifts.
