The Italian Po Valley hail problem is examined and a description is presented of its economic, dimensions, its climatology, and some of the meteorological factors which influence it. A brief history of hail prevention in Italy is presented, covering ancient beginnings and tracing the development of the use of explosives employed by farmers at the present time in the Po Valley. Italy has the worst hail problem in the world, the estimated average low being $1333 per square mile W annum, nationwide, with an average loss reaching $7106 per square mile on a smaller scale in the Po Valley of North Italy. The great crop loss to hail is not due to excessively frequent hall. Point and areal hail-day frequencies are lower than many other hail areas in the world. The great loss value is due to a combination of 1) high crop value, 2) high hall frequency during the growth season, 3) storms that are large in areal extent, 4) frequent large hail, 5) long hailfall durations, and 6) large numbers of hailstones per square foot. The meteorological cause is found in the unique terrain configuration of the Po Valley and the cyclonic development which it causes during the passage of synoptic systems.