  The AdS/CFT correspondence has developed over the last years into a very
useful and powerful tool for studying strongly coupled field theories at finite
temperature and density. Of particular interest is the regime of near
equilibrium real time evolution that can be captured via linear response
theory. The AdS/CFT correspondence allows the calculation of retarded two point
functions of gauge invariant operators by studying fluctuations around
asymptotically AdS black holes. A major role is played by the poles of these
holographic response functions: the quasinormal frequencies. I will review the
applications of these ideas to the hydrodynamics of the strongly coupled quark
gluon plasma and the holographic realization of strongly coupled superfluids.
