AbstractSurf zone processes are one of the most difficult and challenging topics in modern marine science and technology. Because of their scientific and practical (e.g. engineering) importance they have been extensively studied in recent years. Nevertheless, even though the basic equations are known, no complete numerical solution can even be attempted yet. Moreover, there are still many unanswered questions relating to domain definition, well‐posedness of the mathematical problem, validity of closure relationships and stability/convergence aspects of the numerical solution.This paper, starting from the basic conservation laws, derives sets of governing equations for the various flow modes present in the surf zone (currents, waves and turbulence). The emphasis will be on physical principles and simplifying hypotheses to show the application field of the different sets of equations. The paper will concentrate on the form and validity of the equations, including also some comments on discretization and numerical solution technique