Why does the Quark - Gluon Plasma at RHIC behave as a nearly ideal fluid ?

The lecture is a brief review of the following topics: (i) collective flow phenomena in heavy ion collisions. The data from RHIC indicate robust collective flows, well described by hydrodynamics with expected Equation of State. The transport properties turned out to be unexpected, with very small viscosity; (ii) physics of highly excited matter produced in heavy ion collisions at Tc < T < 4Tc is different from weakly coupled quark-gluon plasma because of relatively strong coupling generating bound states of quasiparticles; (iii) wider discussion of other “strongly coupled systems” including strongly coupled supersymmetric theories studied via Maldacena duality, as well as recent progress in trapped atoms with very large scattering length.