The Old World (OW) arenavirus Lassa (LASV) is estimated to infect several hundred thousand people yearly in West Africa, resulting in high numbers of Lassa fever (LF), a viral hemorrhagic fever (HF) disease associated with high morbidity and mortality. To date, no licensed vaccines are available to LASV infections, and anti-LASV drug therapy is limited to an off-label use of ribavirin (Rib) that is only partially effective. The development of reverse genetics has provided investigators with a novel and powerful approach for the investigation of the molecular, cell biology, and pathogenesis of LASV. The use of cell-based LASV minigenome (MG) systems has allowed examining the cis- and trans-acting factors involved in genome replication and gene transcription and the identification of novel drugable LASV targets. Likewise, it is now feasible to rescue infectious recombinant (r)LASV entirely from cloned cDNAs containing predetermined mutations in their genomes to investigate virus-host interactions and mechanisms of pathogenesis, as well as to facilitate screens to identify antiviral drugs against LASV and the implementation of novel strategies to develop live-attenuated vaccines (LAV). In this chapter we will summarize the stateof- the-art experimental procedures for implementation of LASV reverse genetics. In addition, we will briefly discuss some significant translational research developments that have been made possible upon the development of LASV reverse genetics.