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 ...