HIV virology and pathogenetic mechanisms of infection are continuously being investigated. A detailed understanding of HIV structure and how it establishes infection and causes AIDS are crucial not only to identify and develop new effective drugs and vaccines, but also to define strategies for the laboratory diagnosis of HIV infection. HIV testing is a critical step that allows to control HIV spreading in the population. Laboratory diagnostic strategies have to be continuously revised according to new discoveries on the replication characteristics and the pathogenetic mechanisms of HIV infection.