Polarization in QCD

We first deal with the muon anomalous magnetic moment which is found to differ from the standard model prediction by 2.7 σ. A new proposal will aim at reducing the error by a factor 2. The main part of the paper then deals with the spin structure of the nucleon which can be studied in terms of quark and gluon helicity distributions, quark transversity distributions and generalized parton distributions. The main recent results are first indications that the total gluon spin in the nucleon might be small and a first measurement of the Collins fragmentation function which is needed to extract transversity distributions from semi-inclusive DIS data