  In this talk I will present some of the main difficulties we encounter in
studying the large scale behavior of disordered systems. This presentation will
be done using a field theory language. The difficulties in applying the
standard renormalization group approach are due to the presence of strong
non-perturbative effects that we do not know how to master. These difficulties
are particular acute in the case of ferromagnets in random field, localized
electrons, growth models and spin glasses. I will review the situation
presenting at the end a promising approach based on fat diagrams.
