This chapter starts with describing statistics of Gauß processes, which result from linear responses to a linearized stationary seaway. Then computing the distribution of nonlinear responses to one or several correlated Gauß processes is illustrated for an example. For more general nonlinear cases, simulation cannot be avoided, but this may require excessive time for directly counting the rate with which seldom occurring events like capsizing or extreme loads occur. A technique for reducing the effort of such computations by orders of magnitude is based on the fact that similar wave events occur in seaways of different significant heights with rates differing by known factors. Finally, the superposition of probability distributions for stationary seaways to long-term distributions and the concept of design waves is described.