Quenching of single-particle strength from direct reactions with stable and rare-isotope beams

In this review article we discuss the present status of direct nuclear reactions and the nuclear structure aspects one can study with them. We discuss the spectroscopic information we can assess in experiments involving transfer reactions, heavy-ion-induced knockout reactions and quasifree scattering with $(p,2p)$, $(p,pn)$, and $(e,e^{\prime }p)$ reactions. In particular, we focus on the proton-to-neutron asymmetry of the quenching of the spectroscopic strength.