HIV-1 super infection in humans have been reported since 2002. Super infection is defined as the reinfection of an individual who already has an established infection with a heterologous HIV strain. Controversy exists surrounding superinfection, because it has implications concerning our understanding of worldwide HIV diversity, individual immunity and disease progression, and vaccine development. Here, we review the current understanding of HIV superinfection. The initial published reports involved individuals who were reinfected with a virus that belonged to a clade different from that of the initial infecting virus immune responses to the initial infection might be less likely to be protective against such a divergent superinfecting virus. Subsequently, however, reinfection with a virus that belonged to the same clade as the initial infecting virus (intraclade superinfection) started to be reported.