Human genetic diversity, both common and unusual, increases susceptibility to infectious disease. Epidemiological studies have demonstrated disparities in the prevalence or severity of disease within and between populations exposed to the same infectious agent, demonstrating the importance of genetic background. In population genetic research, the genetic component (susceptibility) in infectious disease determination has been calculated, and certain susceptibility gene(s)/polymorphisms have been found. A vast number of genes appear to influence susceptibility to infectious diseases, and identifying them can provide new molecular targets for preventative and therapeutic interventions as well as provide insights into pathogenic and protective mechanisms. Immunogenetic links to infectious diseases have a lot of promise for guiding immunomodulatory therapies and vaccine development.