Advances in the fields of molecular genetics and genomics have been considerable and these have led to the development of very useful linkage and physical maps of the pig genome. The genetic linkage map now has over 1,900 loci including approximately 300 genes. The physical genetic map has over 1,000 loci including a growing number of known genes. The development of new maps including those incorporating large numbers of AFLP markers map are also well underway and will add 2,000 additional markers, bringing the total to nearly 4,000 genes and markers. Several recent quantitative trait loci scans and candidate gene analyses have identified important chromosomal regions and individual genes associated with traits of economic interest in the pig. These include QTL for growth and backfat, meat quality traits, and reproduction. The causative mutations for porcine stress syndrome (HAL or CRC1) and the RN disorder, candidate genes for litter size (ESR, PRLR, RBP4), growth (MC4R), meat quality (hFABP, aFABP), disease resistance (FUTI, SLA, NRAMP), and coat color (KIT, MC1R) have also been identified. The commercial pig industry is actively using this information and in‑house research to improve pig production by marker assisted selection (MAS). Furthermore, research to study the co expression of hundreds of genes is now beginning. This research will aid in our understanding of genetic systems and how to alter their relationships to improve pig production.