There are many classes of waves in the ocean, ranging from small-scale surface waves to planetary scale topographic and Rossby waves. Especially for the small-scale waves it is often necessary to account of strongly nonlinear eects. This talk will review some of the theoretical modelling of nonlinear waves, looking in particular at rogue waves, tsunamis and large-amplitude internal waves in coastal seas. Emphasis will be placed on the role of canonical model equations such as the nonlinear Schrodinger equaltion, the Korteweg-de Vries equation and the extended Korteweg-de Vries (Gardner) equation, sometimes with vari-able coecients. For the nonlinear Schrodinger equation, we will describe how breather solutions play a central role in modelling rogue waves in deep water.For tsunamis, we will describe how undular bores propagates into shallow water,and the possible role of breather solutions in describing depression waves. Then,we will describe how variable topography and polarity reversal can cause the disintegration of an internal wave solitary waves in the coastal ocean.