The coastal ocean extends from the land-sea interface where freshwater enters the ocean through rivers and estuaries to beyond the continental shelf. Due in part to its shallow and complex bathymetry and coastline, the coastal ocean is quite dynamic and can feature large waves and currents driven by atmospheric storms and ocean tides, and large changes in water temperature and salinity due to seasonal changes in the surface weather and river runoff. The coastal ocean is also extremely productive, supporting a rich and diverse ecosystem and many major fisheries. With increasing human use and exploitation of the coastal ocean, scientific interest in understanding and predicting coastal ocean processes has increased dramatically. The first ocean circulation model designed specifically for coastal application—the Princeton Ocean Model (POM) developed by Blumberg and Mellor (1987)—led immediately to new understanding of a number of important physical phenomena driven by tidal and wind forcing and provided the first core model for coupled physical-biological modeling. Although POM and the development of other coastal ocean circulation models have advanced coastal ocean science significantly in the last 25 years, these existing models have limitations that prevent their universal application in the coastal ocean.