---------------------------------------------------------------------- `Relativistic Conformal Magneto-Hydrodynamics from Holography' Abstract: I will review the principles of relativistic hydrodynamics viewed as effective field theory and the holographic approach to it. Then I will use the AdS/CFT correspondence to study first order relativistic conformal hydrodynamics of (2+1)-dim. magnetic fluids. I will show that the phenomenological approach based on the principle of the positivity of the entropy production is violated in magneto-hydrodynamics already at the linearized level. This is established by studying the strongly coupled M2-brane fluid in external magnetic field. ----------------------------------------------------------------------