It was recently realized that the understanding of fluctuations, in particular fluctuations in the
initial state, is an essential ingredient in the analyses of ultra-relativistic heavy-ion collisions.
Several selected effects with respect to initial state fluctuations and the corresponding harmonic
flow will be addressed in this talk, including the generation of higher order harmonic flow, flow
phase correlations, and fluctuations of harmonic flow. In the framework of hydrodynamics,
analyses of these effects can be made to extract the dynamical property of the de-confined
quark-gluon medium.