  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'p) reactions. In particular, we focus on the
proton-to-neutron asymmetry of the quenching of the spectroscopic strength.
