Understanding the wave-current interactions (WCI) is crucial to accurate modelling of wave, tides and storm surge in the coastal oceans. In this talk, I will use case studies to show WCI can greatly modify sea level and wave height via tide-induced water level changes and current advection/refraction of wave energy. More specifically, model results show that WCI affects wave set-up in the surf zone due to a balance between cross-shore pressure gradient and wave radiations stress gradient. Furthermore, the water level is the dominant factor in significant wave height modulation when the wave propagates into shallower regions from the deeper ocean, whereas the current modulates the deep ocean wave height. Wave energy dissipation related to whitecapping processes plays a greater role in reducing the wave height nearshore than the dissipation due to depth-induced breaking and bottom friction.