The soybean cyst nematode (SCN), Heterodera glycines, is a chronic problem for soybean production in Wisconsin. The distribution of SCN expands every year. This nematode rarely disappears from a field once an infestation is detected, even if SCN-resistant soybean varieties are incorporated into the rotation. Host resistance is the most effective and economical management strategy available for this soybean pest, but even this tactic must be thoughtfully deployed to achieve full yield potential. The most serious threat to SCN-resistant varieties is the tremendous genetic variation among the individual nematodes that comprise a SCN population. Somewhere “in the crowd” lurks nematodes not affected by the host chemistry that confers resistance to nematode reproduction. The fact that the majority of nematodes are affected explains why host resistance is successful in boosting yields; the fact that some are not explains why it is difficult to maintain high yields if the same soybean genotype is planted season after season.