The practical importance of wind-wave interactions can hardly be overstated. Activities at sea and on the coast depend on accurate wind and wave forecasts and statistics, from planning shipping activities to designing dikes and harbors. Because waves are only weakly nonlinear, they lend themselves to elegant mathematical descriptions that reach an accuracy not often found when dealing with the fluid envelopes of our planet. Yet, in spite of the common experience of the casual observer that waves are generated by the wind, grow, and break, a quantitative description of the processes involved is extremely difficult. Further, if wave conditions depend obviously on the wind fields, winds and weather systems are in turn are affected by the waves.