Anisotropic collective phenomena in ultra-relativistic nuclear collisions

For a detailed review of this subject I refer to a recent paper [S.A. Voloshin, A.M. Poskanzer and R. Snellings, arXiv:0809.2949 [nucl-ex]]; in this talk I only very briefly comment on a few most important questions: (a) Very recent significant progress in viscous hydrodynamics calculations. (b) Initial eccentricity/flow fluctuations, the effect of which has been clarified recently. (c) Initial conditions, in particular the role of the gradients in the initial velocity field. (d) Puzzling system size dependence of directed flow. (e) Azimuthal correlations that are sensitive to the strong parity violation. (f) Future measurements at RHIC and LHC, including pp-collisions.