In response to favorable corn (Zea mays L.) prices, corn area in the U.S. has increased while soybean [Glycine max (L.) Merrill.] area has decreased over the past decade; in 2012, corn occupied 30.4 million ha in the U.S. Corn Belt compared to 24.5 M ha of soybean. We have established several long-term crop rotation studies to see how corn and soybean yields compare when each crop follows itself or another crop or crops in sequence. Over 15 years (1998 to 2012) at a productive Illinois site (Monmouth), corn following soybean in a 2-yr rotation or following wheat (Triticum aestivum L.) or soybean in a 3-yr rotation yielded 2.9 t/ha (30%) more than continuous corn. Soybean following corn in a 2-yr rotation or following corn or wheat in a 3-yr rotation yielded 0.58 t/ha (15%) more than continuous soybean, and soybean in the 3-yr rotations yielded 0.3 t/ha (7%) more than soybean in the corn-soybean rotation. Tillage increased corn and wheat yields, but not soybean yields. The corn-soybean 2-yr rotation was most profitable. At Perry, corn following soybean or wheat yielded 1.6 t/ha (17%) more than continuous corn, and the effect of rotation on soybean yield was not significant. Tillage effects and relative returns to rotation and tillage were similar to those at Monmouth. We did not find consistent trends in rotation effects on yield over years at either location. These results show larger yield penalties and less yield stability for continuous corn than are normally expected, and show only modest yield benefits from including wheat in rotation with corn and soybean. Economically, the corn-soybean rotation appears to provide better returns with current crop prices than other rotations tested. Within this rotation, no-till provides returns equal to or higher than those with tillage due to lower costs.