Sulfur deficiencies in crop production are increasing for several reasons: increasing use of S-free fertilizers; decreasing use of S as a pesticide; increasing crop yields requiring greater amounts of plant nutrients. A 4th possible factor, atmospheric supplies of S, was considered. The functions of S as a plant nutrient were discussed and examples were given of crop responses resulting from the application of this element. The various sources of fertilizer S were enumerated. The role of S in animal nutrition was briefly considered and the importance of an adequate supply of dietary S for the effective utilization of nitrogen by ruminants was pointed out.