Increased emphasis has been placed on the characterization of domestic animal genomes and performance as a new method to further improve the selection of animals. Despite its scientific immaturity, the rapid progress made in animal genome mapping has already exceeded expectations. For cattle, four linkage and two cytogenetic maps have been produced. Several monogenic traits have been characterized at the DNA level and the identification of loci influencing polygenic traits has been intensively studied worldwide. Using DNA markers to improve the genetic performance of animals for the economic traits such as growth, carcass quality, milk production, reproduction, and disease resistance will become an important aspect of animal breeding.