In Chap. 19 , we have examined the response of a floating structure about each of its six degrees of freedom when excited by regular waves with a single frequency and amplitude approaching from any arbitrary direction. Clearly, this behavior is not representative of real-world conditions where incoming waves exhibit a wide range of frequencies and amplitudes. To facilitate the design of floating structures that guarantee the comfort of its occupants, the maximum response and accelerations excited by irregular waves must be determined.