Water wave problems are of interest to coastal engineers, marine and offshore engineers, engineers working on naval architecture and ship design, and scientists working on physical oceanography and marine hydrodynamics. The theoretical study of water waves can be traced back to two centuries ago. In the past few decades, research in water waves has been very active, driven by the increasing demand of sea transport and offshore oil exploration. Various water wave theories have been developed to describe different wave phenomena. These wave theories enable us to understand the physical mechanisms of water waves and provide the basis for various water wave models. Historically, the techniques of water wave modeling were developed in mainly two areas, coastal engineering and offshore engineering (including naval architecture). While the traditional wave modeling in coastal engineering has emphasised detailed wave transformation over a rigid and fixed bottom or structure, the wave modeling in offshore engineering and naval architecture has focused on wave loads on relatively large bodies and the corresponding structure responses. In recent years, there has been a trend to couple the modeling of complicated wave transformation (e.g., wave breaking) with the analysis of body motion. Furthermore, efforts are also being made to develop general-purpose models that can be applied not only to water wave problems, but also to many other types of turbulent-free surface flow problems (e.g., river flows, mold filling).