  Recent progress in laser and x-ray spectroscopy of muonic atoms offers
promising long-term possibilities at the intersection of atomic, nuclear and
particle physics. In muonic hydrogen, laser spectroscopy measurements will
determine the ground-state hyperfine splitting (HFS) and additionally improve
the Lamb shift by a factor of 5. Precision spectroscopy with cryogenic
microcalorimeters has the potential to significantly improve the charge radii
of the light nuclei in the $Z=3-8$ range. Complementary progress in precision
should be achieved on the theory of nucleon- and nuclear-structure effects. The
impact of this muonic-atom spectroscopy program will be amplified by the
upcoming results from H and He$^+$ spectroscopy, simple molecules such as
HD$^+$ and Penning trap measurements. In this broader context, one can test
ab-initio nuclear theories, bound-state QED for two- or three-body systems, and
determine fundamental constants, such as the Rydberg ($R_\infty$) and the
fine-structure ($\alpha$) constants.
