Cancer is a group of more than 100 diseases in which cells display uncontrolled growth, invasion, and sometimes metastasis. Milk and dairy products contain micronutrients and several bioactive constituents that may influence cancer risk and progression. Much of the focus of human, population-based studies has been on the effects of intake of milk and total dairy products or of calcium intake. Based on a systematic review of the epidemiologic literature, the World Cancer Research Fund and American Institute for Cancer Research report concluded there was a probable association between milk intake and lower risk of colorectal cancer, a probable association between diets high in calcium and increased risk of prostate cancer, and limited evidence of an association between milk intake and lower risk of bladder cancer. For other cancers, the evidence was mixed or lacking. Since the 2007 report, several additional, large-cohort studies have been published, including two that show an inverse association between intake of cultured dairy products and bladder cancer. Little is known about the potential effect of various bioactives produced during rumen microbe metabolism on cancer risk. Furthermore, studies support a role of live microbes present in some dairy products in the modulation of the human gut microbial community and gut metabolism. Given the growing appreciation for the role of the gut microbial community in relation to immune function and health and disease, including cancer, the potential role of various dairy products in the modulation of the human gut microbiome warrants further evaluation. Key teaching points: As a dietary exposure, dairy products are a complex group of foods and composition varies by region, which makes evaluation of their association with disease risk difficult. For most cancers, associations between cancer risk and intake of milk and dairy products have been examined only in a small number of cohort studies, and data are inconsistent or lacking. Meta-analyses of cohort data available to date support an inverse association between milk intake and risk of colorectal and bladder cancer and a positive association between diets high in calcium and risk of prostate cancer. Other constituents of dairy products, such as rumen-derived metabolites, have not been evaluated extensively for cancer-preventive properties. The influence of live microbes in fermented dairy products and certain cheeses on the human gut microbiome and immune function is a growing area of study.