Book excerpt: Wave effects on coastal and offshore structures have been studied for more than two decades. Nevertheless, the dynamic behaviors of those structures due to a real sea state, considering the features of randomness, nonlinearity, and directionality, have seldom been investigated. In this report, random and nonlinear wave effects on those structures have been examined analytically. The first part presents a new model of a linear random wave force transformation on a sloping beach as the waves propagate from offshore toward the shore. The second part investigates the effect of nonlinear wave interactions on the dynamic response of a fixed offshore structure. The third part examines the effect of wave groups and an associated forced second-order wave system on the dynamic response of a fixed offshore structure. The results of this report show that random and nonlinear waves play important roles on the dynamic behaviors of coastal and offshore structures. Keywords: Ocean waves, Coastal structures; Random waves; Wave force transformation.