For much of the world, control of internal and external parasites is as, or even more, important than controlling infectious diseases. Cattle parasites can severely affect production, overall health, and even cause direct death loss. They are also involved in transmitting other diseases, and some parasites have direct immunosuppressive activity. Immune responses against parasites are often complex, incomplete, and non-protective. However, immunologic research continues to be performed, as vaccination may provide a long-term solution to controlling many of these parasites.