Genetic variability of mastitis resistance is well established in dairy cattle.Many studies focused on polygenic variation of the trait, by estimatingheritabilities and genetic correlation among phenotypic traits related tomastitis such as somatic cell counts and clinical cases. The role of MajorHistocompatibility Complex in the susceptibility or resistance to intrammamaryinfection is also well documented. Finally, development from molecular genomemapping led to accumulating information of quantitative trait loci (QTL) relatedto mastitis resistance and better understanding of the genetic determinism ofthe trait. From economic and genetic analyses, and according to welfare and foodsafety considerations and to breeders and consumer's concern, there is more andmore evidence that mastitis should be included in breeding objective of dairycattle breeds. Many countries have implemented selection for mastitis resistancebased on linear decrease of somatic cell counts. Given biological questioning,potential unfavourable consequences for very low cell counts cows are regularlyinvestigated. Improvement of selection accuracy for mastitis resistance isongoing and includes: advances in modelling, optimal combination of mastitisrelated traits and associated predictors, such as udder morphology, definitionof global breeding objective including production and functional traits, andinclusion of molecular information that is now available from QTL experiments.