Cattle have adapted to survive in a wide variety of environments, which has given rise to extensive diversity at the phenotypic and genetic level. Today, this diversity provides the opportunity for selective breeding and improvement of cattle for commercially desirable traits. Up to now, selection has been based on phenotype, focusing on the traits that are most easily measured. This approach has been successful, with spectacular improvement in some traits, although there have also been associated penalties for other traits. However, intensive selection based on a limited number of phenotypes could reduce the diversity present in the population, which may have important implications for the success of future breeding objectives. In addition, selective improvement has been focused on a limited number of breeds, which are now used internationally, with the consequence that many of the genetically different breeds of cattle are being lost worldwide. To make the selection process more efficient, it is important to gain knowledge of the genes controlling particular traits and to understand the way that variation within these genes affects the traits. The first step toward identifying the trait genes has been to develop genetic and physical maps of the bovine genome. This has been achieved at an international level using several genome-mapping methods. The ultimate genome map, the bovine genome sequence, is now being determined. This genomic information is being used in specific cattle populations to identify, first the genetic location of genes controlling particular traits, then, starting from the genomic locations, to identify the genes themselves. Knowledge of the genes controlling complex traits, such as feed-conversion efficiency, health, fertility, and product quality, would allow these traits to be included in breeding objectives, with the potential for improved commercial viability, while safeguarding welfare and genetic diversity. Keywords: Genome; Genotype; Marker-assisted Selection (MAS); Microsatellite Loci; Phenotype; Quantitative trait loci (QTL); Selection; Trait