Wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is a major disease of wheat worldwide. Enhancing resistance is a major objective in wheat breeding programs due to the devastating economic losses caused during stem rust epidemics. To increase genetic diversity in U.S. spring wheat breeding programs, a nested association mapping (NAM) population was developed by crossing 25 exotic accessions selected from the USDA-ARS Spring Wheat Core Collection with RB07, a Minnesota cultivar selected as the common parent because it has wide adaptation in the region. The 25 exotic parents were screened for seedling resistance to Pgt races TTTTF, TPMKC, HJHKC, TTKSK, TTKST, TRTTF, TTKTT, and TTKSF+Sr9h. Two of the parents (PI 519465 from Zimbabwe and PI 520033 from Kenya) were resistant to all the races evaluated. The two NAM families from the crosses PI 519465/RB07 and PI 520033/RB07 were screened against Pgt races TTKSK, TTKST, TTKTT, TRTTF, and TTKSF+Sr9h and segregated in response to all of them. In the PI 519465/RB07 population, the frequency of resistance varied between 16.9% (TRTTF) and 62.9% (TTKSF+Sr9h). In the PI 520033/RB07 population, the frequency of resistance varied between 36.5% (TRTTF) and 84.7% (TTKSF+Sr9h). Single nucleotide polymorphism (SNP) markers were generated for both families by the genotyping-by-sequencing platform. SNP reads were aligned against the new Chinese Spring wheat genome assembly to obtain physical distances for all markers. To identify genetic variants associated with the resistance, quantitative trait loci mapping is in progress in the combined and individual. families. Selected lines from the two NAM families are broadly resistant against all of the Pgt races in the Ug99 lineage and are in the genetic background of a spring wheat cultivar adapted to the northern Great Plains.