This thesis describes the genetics of carcass composition and pork quality traits. A large population of commercial finishers was extensively phenotyped for growth, carcass composition and meat quality traits. Genetic parameters were estimated based on those measurements. The population was genotyped using 73 microsatellite markers covering approximately 50 percent of the genome. The covered genome regions were pre-selected based on published QTL for carcass composition and meat quality traits that were mainly obtained from divergent crosses. Significant evidence for QTL was obtained. Although with chromosome-wise significance values of 5% the obtained evidence was not very strong despite the large population size. Additional half-sib families and markers were typed to validate and further investigate the map position of QTL identified in regions on chromosomes 2, 4, 11, 13 and 14. A variance component (VC) analysis method using linkage and linkage disequilibrium was applied to further characterize and refine the map position of the QTL. The results were compared with results obtained by the classic regression analysis method. The VC analysis results reveal the considerable contribution of the dam haplotypes to the variance of meat quality traits. An accurate positioning of the QTL however was not yet possible with the marker density so far. Therefore, new microsatellites were developed by in silico analysis of BAC-end sequences (BES) of BACs on the porcine physical map and genomic shotgun sequences. This resulted in the identification of thousands of new markers covering the porcine genome with over 200 new markers in the region of interest on SSC4. The ~200 markers were tested and resulted in ~60 markers that were informative and used in an effort to further fine mapping of the QTL on SSC4.