  Nonperturbative approximation schemes based on two-particle irreducible (2PI)
effective actions provide an important means for our current understanding of
(non-)equilibrium quantum field theory. A remarkable property is their
renormalizability, since these approximations involve selective summations to
infinite perturbative orders. In this paper we show how to renormalize all
$n$-point functions of the theory, which are given by derivatives of the
2PI-resummed effective action $\Gamma[\phi]$ for scalar fields $\phi$. This
provides a complete description in terms of the generating functional for
renormalized proper vertices, which extends previous prescriptions in the
literature on the renormalization for 2PI effective actions. The importance of
the 2PI-resummed generating functional for proper vertices stems from the fact
that the latter respect all symmetry properties of the theory and, in
particular, Goldstone's theorem in the phase with spontaneous symmetry
breaking. This is important in view of the application of these techniques to
gauge theories, where Ward identities play a crucial role.
