Adequately probing interfacial or (free) surface waves offers the possibility of exploring qualitative and quantitative equilibrium and rheological features hence large scale and long time dynamics. Several experimental techniques are briefly reviewed. The combination of capillary waves experiments with methods based on analyzing the mechanical deformation of the surface allows to explore dynamics from the microsecond scale up to collective phenomena relaxing at very long times, seconds, minutes or even hours. Results related to the scaling behavior of insoluble polymer films, and to the existence of a glass transition in quasi-2D systems are also discussed.