I discuss inclusive and semi-inclusive lepton-hadron scattering emphasizing
the importance of polarization in order to study various single or double spin
asymmetries and the importance of particle identification and angular
resolution in the dectection of final state particles to study azimuthal
asymmetries. The observables obtained in this way enable a detailed study of
quark and gluon correlations in hadrons.Comment: 15 pages LaTex, 20 figures using epsf.sty, revised layout, talk
presented at the second ELFE Workshop, 23-27 September 1996, St. Malo, Franc