The lecture will be concerned with fluctuations at hydrodynamic scales in fluids and fluid mixtures that are out of thermal equilibrium but in the absence of convection or turbulence. The principle of local thermodynamic equilibrium is known to be valid in nonequilibrium thermodynamics for the thermodynamic properties; however, this principle is never valid for the fluctuations of these properties. While hydrodynamic fluctuations in equilibrium fluids are spatially short ranged except for states near a critical point, fluctuations in nonequilibrium fluids are always long ranged, even far away from any hydrodynamic instability. These issues will be illustrated by theoretical and experimental studies of temperature and concentration fluctuation in liquids and liquid mixtures subjected to a temperature gradient.