Welfare is affected by the genetic inheritance that an animal receives and the environment in which it is kept. The focus of this chapter is on the contribution of genetics to animal welfare and how this may be harnessed to improve the welfare of animals. The genetic structure of a domestic breed is determined by its early history and the existence of a hierarchical breeding structure that combine to increase homozygosity. This may decrease health and welfare, as well as productivity through inbreeding depression and by increasing the prevalence of genetic disease. In most farm animals, these processes are alleviated by the use of crossbreeding, which should be more widely practised in companion animals. Genetic selection may adversely affect welfare through inappropriate selection criteria, as in many breeds of dog, either inadvertently because of unexpected genetic correlations, or as a result of the neglect of important fitness traits. Many factors constrain selection by animal breeders - such as time, the number of potential traits, negative genetic correlations between economic and welfare traits, the costs of measuring and selecting animals and shifting market requirements. Examples of welfare problems, and skeletal and physiological disease. New opportunities for genetic improvement of animal welfare based on DNA markers, new electronic measurement techniques and improved statistical procedures are likely to make selection for welfare traits more effective in the near future.