We mention briefly two new results in the study of muonic atoms concerning the measurement of spectroscopic quadrupole moments and the study of radiative corrections with muonic atoms. As an introduction to the subject proper, we review shortly some of the basic properties of hadronic atoms and their theoretical analysis. We then discuss some applications to the study of the nucleus (neutron distributions, quadrupole mass densities) as well as novel applications to the investigation of properties of the captured particle (polarizability) or of the particle-nucleon scattering amplitude in the nucleus (off-shell extrapolation and correlation effects).