Color strings, pomeron shadowing and Color Glass Condensate

In the recent experiments like DIS at HERA or the heavy-ion experiments at RHIC, and also in expected LHC at CERN, the number of involved partons is very large, due to the high energy and/or the high number of participants of those experiments. These high parton densities should in principal lead to an extremely huge multiparticle production, but experimentally we have seen that this is not the case. So there should be a mechanism that reduces the number of created particle. Two kind of phenomena have been proposed. On one side there is the possibility of saturation in the initial state of the collision. On the othe side, there is the proposal of the creation of a Quark Gluon Plasma, and it has been presented as a final state interaction mechanism. Here, I review the problem of parton saturation and its implications through three in principal different approaches, but somewhat related: saturation in a geometrical approach, QCD saturation through the Color Glass Condensate and shadowing in a Pomeron approach.