The different approaches to genetic improvement of shellfish include polyploidization, hybridization and selection. Polyploidization has the most potential for immediate application to commercial breeding as triploid induction has already been achieved for many shellfish species. Comparative performance of triploids versus diploids has been studied in detail in oysters. Hybridizations among species can also be a source of novelty, but interspecific hybrids often show reduced performance compared to their parents. Experimental breeding programmes for disease resistance or growth performance show that heritable variation exists for these traits and that genetic improvement can be achieved by selection. At present, these breeding programmes still have to reach a scale enabling proper genetic diversity management, multi-site testing or effective improvement of the commercial stocks. Public research institutes, commercial bivalve hatcheries and shellfish farmers should cooperate to adopt selective breeding programmes as an integral part of the husbandry of shellfish species.