Prevention and treatment of West Nile virus (WNV) and other flavivirus infections have become a global public health priority. This fact is highlighted by the recent epidemic of WNV in the US. Since the first outbreak of WNV in the US in 1999, the virus has caused over 4000 known human cases and at least 263 human deaths. The epidemic of WNV in the US in 2002 represents the largest meningoencephalitis outbreak in the western hemisphere, and the largest WNV outbreak ever reported. Reverse genetic systems of WNV are extremely useful tools for studying many aspects of the virus, including viral replication, pathogenesis, antiviral therapy and vaccine development. In this review the current status of the reverse genetic systems of WNV and their potential applications are discussed.