Technical Abstract: Aflatoxin contamination costs the U.S. peanut (Arachis hypogaea L.) industry over $20 million annually. The development of peanut cultivars with resistance to preharvest aflatoxin contamination (PAC) would reduce these costs. Screening techniques have been developed that can measure genetic differences in aflatoxin contamination and they have been used to identify accessions that exhibited relatively low PAC in multiple environments. Significant reductions in PAC have been identified in peanut genotypes with drought tolerance. These sources of resistance to PAC have been crossed with cultivars and breeding lines that have high yield, acceptable grade, and resistance to spotted wilt caused by Tomato spotted wilt tospovirus (TSWV). Due to the large environmental variation in PAC, breeding populations can only be evaluated in late generations when there is less heterozygosity and adequate seed are available for field testing using multiple replications. Evaluation of numerous breeding populations has identified several families and individual breeding lines that have relatively low PAC, relatively high yield, and acceptable levels of resistance to TSWV. To increase breeding efficiency, studies on mechanisms of resistance to PAC are being conducted. The most promising mechanisms identified thus far are resistance to drought and resistance to the peanut root-knot nematode. Late generation breeding lines have been developed with resistance to drought, several of which also exhibited reduced aflatoxin contamination in multiple environments. Tifguard, the first cultivar with high levels of resistance to both TSWV and the peanut root-knot nematode [Meloidogyne arenaria (Neal) Chitwood race 1] was released from this program. Testing is ongoing to determine if this cultivar can be used to reduce aflatoxin contamination in nematode infested fields.