Collective effects in nuclear collisions: theory overview

In these proceedings I review recent developments concerning the hydrodynamic description of the quark-gluon plasma (QGP). I report on the progress towards more realistic simulations and discuss new features about the QGP transport coefficients of the hot (and baryon dense) medium formed in heavy ion collisions. A brief discussion is included on the applicability of hydrodynamics and its extension to the far-from-equilibrium regime.