Although soil erosion is a natural process, it has increased to the point where it far exceeds the natural formation of new soil. However, with only occasional exceptions, national agricultural and population policies have failed to take soil depletion into account. Projections of world food production always incorporate estimates of future cropland area, but what has been lacking has been an effort to project changes in inherent productivity of the projected cropland area. To help remedy this shortcoming in world food supply projections, an estimate of the worldwide loss of topsoil from cropland is presented. Areas discussed include: (1) the causes of soil erosion; (2) dimensions of the problem in various countries; (3) the effects of erosion (particularly related to loss of topsoil) on agricultural productivity; (4) the effects of erosion on other areas (indicating that the loss of topsoil that reduces land productivity may also reduce irrigation, electrical generation, and the navigability of waterways); (5) economic aspects of soil conservation; (6) the role of governments; and (7) global aspects of the problem. (JN)