Extracting the QGP viscosity from ...

The successes of ideal hydrodynamics in describing RHIC data at lower p_T region led to the well known announcement that "RHIC Scientists Serve Up Perfect Liquid" (the Quark Gluon Plasma, QGP) In order to answer "How perfect is the QGP fluid?", one needs to extract the QGP viscosity from experimental data. Viscous hydrodynamics is such a tool that could attack this problem and may work in regions where ideal hydrosynamics fails. In this talk, I will report recent progress on causal viscous hydrodynamics and extracting QGP shear viscosity to entropy ratio from RHIC data.