For more than a century, physical oceanographers—those who study the physics of the ocean—have been expanding their ability to interpret oceanic observations. The first crucial step is the application of dynamical equations, the fundamental equations of fluid mechanics. The task of developing dynamical models, written out as equations, is not yet complete. There remain unresolved issues such as turbulence, mixing, and friction, and the appropriate way in which to represent them. Nonetheless, the fundamental equations are well accepted and, in many different case studies, well understood. With especially rapid progress in recent years, oceanographers have developed computer models of ocean currents, just as meteorologists have developed numerical models of winds in the atmosphere.