The current armamentarium for the chemotherapy of viral infections consists of 37 licensed antiviral drugs. For the treatment of human immunodeficiency virus (HIV) infections, 19 compounds have been formally approved: (i) the nucleoside reverse transcriptase inhibitors (NRTIs) zidovudine, didanosine, zalcitabine, stavudine, lamivudine, abacavir and emtricitabine; (ii) the nucleotide reverse transcriptase inhibitor (NtRTI) tenofovir disoproxil fumarate; (iii) the non-nucleoside reverse transcriptase inhibitors (NNRTIs) nevirapine, delavirdine and efavirenz; (iv) the protease inhibitors saquinavir, ritonavir, indinavir, nelfinavir, amprenavir, lopinavir (combined with ritonavir at a 4/1 ratio) and atazanavir; and the viral entry inhibitor enfuvirtide. For the treatment of chronic hepatitis B virus (HBV) infections, lamivudine as well as adefovir dipivoxil have been approved. Among the anti-herpesvirus agents, acyclovir, valaciclovir, penciclovir (when applied topically), famciclovir, idoxuridine and trifluridine (both applied topically) as well as brivudin are used in the treatment of herpes simplex virus (HSV) and/or varicella-zoster virus (VZV) infections; and ganciclovir, valganciclovir, foscarnet, cidofovir and fomivirsen (the latter upon intravitreal injection) have proven useful in the treatment of cytomegalovirus (CMV) infections in immunosuppressed patients (i.e. AIDS patients with CMV retinitis). Following amantadine and rimantadine, the neuraminidase inhibitors zanamivir and oseltamivir have recently become available for the therapy (and prophylaxis) of influenza virus infections. Ribavirin has been used (topically, as aerosol) in the treatment of respiratory syncytial virus (RSV) infections, and the combination of ribavirin with (pegylated) interferon-alpha has received increased acceptance for the treatment of hepatitis C virus (HCV) infections.