Technical Abstract: The study of host immune responses to Mycobacterium avium subsp. paratuberculosis (MAP) is complicated by a number of factors, including the protracted nature of the disease and the stealthy nature of the pathogen. Improved tools for the measurement of immunologic responses in ruminant species, particularly the bovine, a key target species for MAP infection, has allowed the dissection of host immunologic responses to infection to some extent. Noted as one of the more fastidious mycobacteria, infection with MAP is often characterized by periods of subclinical infection extending for 3 to 5 years. Many animals will clear the infection during this period but it is almost impossible to distinguish by current methods animals that have cleared the infection from those that remain infected but are able to control the progression of disease. Escalation of paratuberculosis to a more clinical state marked by diarrhea and weight loss is thought be caused by immune dysfunction. This treatise will focus on a discussion of host immunity after infection with MAP, drawing upon published studies in bovine tuberculosis and other mycobacterial pathogens in order to fill in the gaps of knowledge and improve our understanding of the disease process for paratuberculosis.