Topology in QCD

Topology on the lattice is reviewed. In quenched QCD topological susceptibility chi is fully understood. The Witten-Veneziano mechanism for the eta’ mass is confirmed. The topological susceptibility drops to zero at the deconfining phase transition. Preliminary results are also presented for chi and chi’ in full QCD, and for the spin content of the proton. The only problem there is the difficulty of the usual Hybrid Monte Carlo algorithm to bring topology to equilibrium.