Wild germplasm contains a wealth of alleles, which are useful in modern agriculture. Nested association mapping (NAM) makes use of wild germplasm by developing multi-parental populations after crossing a single elite cultivar to a number of exotic donors. The resulting NAM lines are subsequently characterized through SNP genotyping and quantitative trait phenotyping. Both data sets are finally merged to conduct genome-wide association studies (GWAS) leading to the identification of quantitative trait loci (QTL), which are involved in controlling these traits. This chapter describes the principles of QTL mapping and NAM mapping, and outlines the sequencing the barley genome. The chapter includes a number of detailed barley NAM case studies from around the world. Finally, the chapter looks ahead to future research trends in this area and suggests further reading on the subject.