The ‘Host-Microbiota-interaction lab’ (HMI) focuses on how the microbiota (the collection of micro-organisms in and on our body) contribute to health and disease. We mainly study the intestinal microbiota, and how it shapes the immune system in steady state, and how disturbances in the intestinal microbiota may contribute to immune disorders and cancer. In addition, the gut microbiota composition is a determining factor in many anti-cancer therapies, most notably immune-checkpoint inhibition therapies. Colorectal cancer (CRC) is one of the most prevalent cancers in Western society, and microbiota abnormalities have been causally linked to CRC development and progression, through mechanisms which are insufficiently understood. Using germfree and gnotobiotic mouse models of human disease (including CRC), the HMI lab tries to unravel the mechanisms by which microbiota affect disease development, both positively as negatively. It has become increasingly clear that the gut microbiota is a central regulator of health and disease, affects both cancer development and therapy response. We therefore believe that microbiota interventions open new perspectives for both cancer prevention and therapy.