Vaccination is a critical tool in modern animal production and key to maintaining animal health. Adjuvants affect the immune response by increasing the rate, quantity, or quality of the protective response generated by the target antigens. Although adjuvant technology dates back to the nineteenth century, there was relatively little improvement in adjuvant technology before the late twentieth century. With the discovery of molecular pathways that regulate the timing, quantity, and quality of the immune response, new technologies are focused on bringing safer, more effective, and inexpensive adjuvants to commercial use. Published by Elsevier Inc.