Since its description in 1902, Aujeszky's disease (AD) has become one of the most thoroughly examined viral diseases of swine. The causative agent, Aujeszky's disease virus (ADV), is a neurotropic alphaherpesvirus that produces fatal encephalitis in newborn pigs and a milder syndrome in older animals. In several instances this virus has been used as a test case to examine novel vaccine concepts in swine, including the honor of being the first genetically modified vaccine used in the field. Furthermore, the examination of the immune response to infection or vaccination with this virus has revealed important information about the function of the porcine immune system, including evidence on the existence of a dichotomy between the humoral and cellular immune response in swine. This review presents a summary of research where ADV has been a valuable tool for the development of novel vaccines and has provided information to better understand the immune response of swine to infectious agents.