We usually think of hydrodynamics as a deterministic description of fluid motion. The focus of this talk is on random fluctuations in fluids caused by thermal noise, inherent in systems with dissipation. The interest in this subject is driven by the progress of heavy-ion collision experiments towards the mapping of the QCD phase diagram. In particular, the search for the QCD critical point at RHIC requires quantitative understanding of fluctuations and their dynamics. I will discuss the role of the fluctuations in hydrodynamics and how we can predict their evolution using deterministic equations.