Mastitis (udder inflammation) is considered one of the main health issues in the dairy industry. It is a costly disease that also has an impact on animal welfare, on milk quality, and on farmers’ pleasure in their work. Furthermore, the use of antimicrobial treatments as a result of mastitis – the biggest contributor to antibiotic use in the dairy industry – is undesirable due to the risk of both antibiotic contamination of milk and the development of bacterial resistance. Consequently, mastitis prevention is relevant for animal welfare, for society, the dairy industry, and farmers. Why some farmers, even though it would improve their results, do not implement effective mastitis management practices is not always known. It is assumed that ‘farmer mindset’, including farmers’ attitudes, beliefs, values, knowledge, perceived norms, and perceived self efficacy, influences farmers’ behavior and therefore their herds’ udder health status. Worldwide, several projects have started to influence farmers’ behavior to improve udder health. In 2005, the Dutch Udder Health Centre (UGCN) was established to execute a national program to improve udder health in five years, aiming at better implementation of the current knowledge on mastitis prevention by deploying various communication strategies to reach farmers and to change their mindset. This thesis aims to understand Dutch dairy farmers’ behavior and mindset regarding udder health management and to study the efficacy of various communication strategies. In the studies presented in this thesis, a variety of qualitative and quantitative methods were used, combining social and veterinary sciences to gather data on farmer mindset towards mastitis and data on the efficacy of various communication strategies. In this interdisciplinary and practice-based approach, studies were initiated on the basis of observations and experiences during the execution of the udder health program or on the basis of emerging questions that followed from the previous studies. Results and recommendations derived from the studies were reported to UGCN and as much as possible implemented to further improve the program; this led to a strong interaction between science and practice. The results of this thesis show that farmer mindset is a decisive factor in mastitis prevention. In particular, the perceived level of mastitis problems (i.e. “Do I have a problem?”) as well as the perceived efficacy of preventive measures (i.e. “Can I solve the problem easily?”) are important determinants that need to be addressed in communication strategies. Veterinarians can be important intermediaries in communication about udder health improvement, provided that they are aware of their role as proactive advisor and apply the relevant communication skills. To be effective, a disease program should do more than distribute technical information about best management practices to dairy farmers. Prevention of complex diseases, such as mastitis, requires customized communication strategies as well as an integrated approach between various stakeholders and different scientific disciplines. Such programs need to be supported by a combination of several policy measures to change farm management in the long term, because for example milk price, milk quota, and financial incentives on milk quality norms, such as bonuses and penalties, have a strong influence on farmer mindset. It should therefore be taken into account that farmers are part of, and are influenced by, a wide societal and institutional context. This thesis provides insight into Dutch dairy farmers’ behavior and mindset towards udder health management, and into the way these can be affected by communication strategies. The findings of this thesis can contribute to the optimization of future programs designed to control and prevent livestock diseases.