Lentiviruses comprise a genus of diverse viruses in the Retroviridae family which are united in their ability to infect and persist in macrophages. Infections are characterized by immune system dysfunctions following sometimes lengthy incubation periods. The viruses in this genus include primate lentiviruses, such as HIV, as well as animal lentiviruses, including equine infectious anemia virus (EIAV). An intriguing feature of lentiviruses is their ability to hijack macrophages so that they are simultaneously involved in the dissemination and control of virus spread throughout the host, leading to disease induction and/or transmission to a new host. Macrophage biology is at an exciting stage with a wealth of new information being generated, as their role is dissected in parasitic, viral, and bacterial infections, as well as in chronic inflammatory and autoimmune disease. Despite the devastating infections that lentiviruses cause, they also have enormous potential as research tools due t