Breaking of wind-generated waves was studies in a laboratory tank. The critical surface slope and global wave steepness for inception of breaking were evaluated. Besides the frequency of occurrence, two other characteristic quantities, height and duration of breaking, were measured. The frequency of breaking was found to increase rapidly with wind velocity, following a power law U2.2. The period of breaking remained about 7% of the wave period at all wind velocities. The height of breaking was about 30% of the wave height. Portions of these results compare favorably with other available measurements.