The 2 - particle irreducible effective action in gauge theories
  The goal of this paper is to develop the formalism of the two-particle irreducible (2PI) \cite{LW61} (or Cornwall - Jackiw - Tomboulis (CJT) \cite {CJT}) effective action (EA) in a way appropiate to its application to non equilibrium gauge theories. We hope this review article will stimulate new work into this field. 
E. Calzetta