Wave groups are a normal occurrence in the real oceans where a group is simply a sequence of several successive waves of greater than average height. Their occurrence may be explained by imagining the real random sea to be composed of a large number of regular waves of different amplitudes, frequencies and random phasing. When a number of the larger components, that is, those grouped around the peak of the spectrum, occur nearly in phase with one another, their amplitudes will reinforce and a group of higher waves, having an average frequency near that of the spectral peak will result. As a result of the relation between wave length and celerity, the different components will, after a time, disperse so that phase coincidence no longer holds. The group is seen therefore, to be of an evanescent nature, continually forming and dissipating.