The chapter starts from the equilibrium problem of a caisson breakwater, and it recalls how stability is examined. It shows Goda's model (GM) for the estimate of the largest load in a given sea state. Then, the chapter introduces fresh results of an extensive small-scale field experiment. These results support GM for the positive wave loads. As for the negative wave loads (those exerted by wave troughs), the chapter suggests using the linear theory with a virtual wave height. The chapter concludes with two worked examples of vertical breakwaters on water depth of, respectively, of 18 and 54 m.