Breast cancer is the most common type of cancer in women. A number of inflammatory molecules play a role in the development of breast cancer, including a family of six proteins, collectively referred as interleukin 17 (IL-17) which are involved in the control of infection, amongst other conditions. Dysregulation of IL-17 levels may result in the development of chronic inflammatory disease. In cancer, IL-17 promotes tumour proliferation, invasion and migration. Elevated IL-17 levels are associated with poor prognosis in breast cancer and are correlated with increased levels of immune checkpoint inhibitors. These data underscore IL-17 as a potential target, alone or in combination with other therapies, against breast cancer. This review presents our current knowledge of the different roles of each member of IL-17 in breast cancer.