Institut de recherche sur les lois fondamentales de l'Univers

The exploration of the inner structure of the
nucleon is a classic topic of nuclear and particle
physics.  Over the last two decades a particular
focus in this field has been on the spin of the
proton and its relation to the angular momenta of the
quark and gluon constituents. In inelastic scattering
of leptons off polarized nucleons it was found that
surprisingly little of the proton spin is carried by the
quark and anti-quark spins. This has triggered much theoretical
progress, and led to new experiments dedicated to unraveling
the proton spin structure, in both lepton-nucleon and
proton-proton scattering. The talk describes
some of the recent results and theoretical progress 

on the nucleon's spin-dependent quark and gluon 

distributions.