This chapter reviews the current understanding of this parasitoid/virus system, describing both experimental approaches and theoretical studies. It suggests that virus-induced superparasitism manipulation may be common since the theoretical model used predicts that all parasitoid infectious viruses of the genital tract would be selected for the enhancement of the natural superparasitism tendency of their parasitoid host. A fundamental feature of viruses is their ability to colonize new cells or individuals through horizontal transmission. It is highly probable that most viruses found in the reproductive tract of parasitoids have the capacity to be horizontally transmitted. Some virus lineages may have lost this capacity, like polydnaviruses, but horizontal transmission might have played a crucial role during their evolution. The results obtained on the LbFV/L. boulardi interaction indicate that horizontal transmission between parasitoid lineages is permitted by the occurrence of superparasitism. Subsequently, natural selection has favored the emergence of a parasitic strategy manipulating the occurrence of superparasitism behavior.