  Probably the most enticing observation in theoretical physics during the last
decade was the discovery of the great amount of consequences obtained from the
AdS/CFT conjecture put forward by Maldacena. In this work we review how this
correspondence can be used to address hydrodynamic properties such as the
viscosity of some strongly interacting systems. We also employ the Boltzmann
equation for those systems closer to low-energy QCD, and argue that this kind
of transport coefficients can be related to phase transitions, in particular
the QGP/hadronic phase transition studied in heavy ion collisions.
