Crop rotation is a universal management practice that has been recognized and exploited for centuries and is a proven process that increases crop yields (Bhowmik and Doll, 1982; Fahad et al., 1982; Baird and Benard, 1984; Dabney et al., 1988; Peterson and Varvel, 1989). Biennial rotation of two summer crops often improves the yield of both crops. In the Midwestern U.S., a biennial rotation of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] produced significant increases in the yields of both crops (Crookston and Kurle, 1989; Meese et al., 1991). Crookston et al. (1988) concluded that the rotation effect is not due to some lingering positive effect of the previous crop. Rather, a rotated crop apparently serves to relieve the negative effect of continuous cropping, and does not make any positive, growth-regulatory contribution to the yield of a following crop. This paper summarizes some of the recent crop rotation data collected in Wisconsin.