Mastitis is a disease that all dairies encounter. While the majority of financial losses from mastitis on dairy farms can be attributed to decreased milk production, the negative impact of mastitis on reproductive efficiency and function in dairy cattle is often overlooked. Multiple observational studies have examined the correlation between measures of fertility and the presence of clinical or subclinical mastitis. Reproductive efficiency measurements such as services per conception and days open are negatively influenced by mastitis. Large clinical studies have demonstrated that cows with clinical or subclinical mastitis are at a greater risk for aborting an existing pregnancy. This risk was greatest if infection occurred during the first 45 d of gestation. The effects of mastitis-causing pathogens on fertility are still an area of active investigation. Researchers have proposed various mechanisms to explain mastitis-induced infertility and have estimated economic losses to producers. Although economic impacts differ among dairies, it is clear that mastitis is an important contributor to poor fertility and represents a significant source of financial loss to dairy operations. As producers seek to limit these losses, measures to prevent mastitis and encourage good health in the transition period and during early lactation will become even more valuable.