*Good* KAM theory books

Andrea85

Hi all, I've read the last capters of Arnold's "mathematical methods of classic mechanics" (so I know the basic facts about differential and symplectic manifolds and the Liouville-Arnold theorem) but this didn't give me enough background to go through KAM theorem: I don't know which is a "resonant" torus, I have not clear in which sense periodic orbits are dense on the torus, so I really can't properly understand this theorem. What should I read further? Which are the best books providing the necessary background to master KAM theory?