Since the 1970’s, several developments have raised high expectations for the use of molecular genetic technology to enhance selection in livestock through application of marker-assisted selection (MAS). These include the discovery of technologies that enabled identification and genotyping of large numbers of genetic markers, and research and statistical methods that demonstrated how these technologies can be used to identify genomic regions that control quantitative traits and how the resulting quantitative trait loci (QTL) can be used in MAS. Yet, to date, the application of MAS in livestock has been limited (see e.g. review in Dekkers 2004). Recent further advances in technology, including genome sequencing and the associated discovery and identification of large numbers of single nucleotide polymorphisms (SNPs) that can be used as genetic markers, combined with the development of high-throughput SNP genotyping that allows the genotyping of large numbers of individuals for large numbers of SNPs at substantially reduced costs, have however stimulated a renewed interest in the large-scale application of MAS in livestock.