[en] The rare muon absorption mode A(Z)(μ^-, v_μγ)A(Z - 1) is but one example for a radiative process, in which additional information hidden in the more abundant parent process, in this case ordinary muon capture A(Z)μ^-, v_μA(Z - 1) can be obtained. The common bremsstrahlung of the external charges contributes little to the high energy part of the photon spectrum. The principal source of radiation here is the intermediate pion, which is exchanged between the hadronic unclear vertex and the lepton pair. The yield and the angular distribution with respect to the muon spin are therefore governed by the strength of the induced pseudoscalar coupling (g_p), which is also mediated by the pionic current. Since the present understanding of this coupling is limited for free as well as for bound nucleons, radiative muon capture experiments continue to be justified. The inherent difficulty of these experiments caused by low yield and adverse background conditions has restricted until recently the experiments to ⁴⁰Ca, a few heavy nuclei, and very limited information for light systems. The comparison of the theoretical predictions with data for nuclei with A ≥ 40 indicates a strong quenching of g_p compared to the albeit imprecise nucleonic value g_p/g_a = 7.0 ± 1.5. However, the interpretation of these results, which for ⁴⁰Ca are confirmed by four experiments, has been met with criticism because the nuclear models used tend to describe the final states in a rather global way, but are needed since the data give only an integrated yield. With the new data on ¹⁸O we are now in a more favorable situation