The National Institute of Allergy and Infectious Diseases (NIAID) supports a wide range of basic and applied research in virology to enhance understanding of viral biology, pathogenesis, and immunology, aiming to prevent, control, and treat viral diseases. Research areas include the viral replication cycle, viral structure and function, host-virus interactions, viral genetics and evolution, viral interference, virus vector relationships, epidemiology, and preclinical and clinical research for vaccines, adjuvants, therapeutics, and diagnostics. NIAID also prioritizes research on the emergence of new epidemic viruses through host switching. The NIAID Antiviral Testing Program evaluates the efficacy and toxicity of new antiviral agents using in vitro assays and in vivo animal models. It focuses on identifying antiviral agents for public health important infections, including newly emerging ones. The program includes various viruses and models, such as herpesviruses, respiratory viruses, papillomaviruses, and biodefense viruses. Animal models include HCV, herpesviruses, respiratory viruses, hepatitis viruses, papillomaviruses, and biodefense viruses. The Collaborative Antiviral Study Group (CASG) is a multi-institutional network funded by NIAID to conduct clinical trials and evaluate experimental therapies for viral infections. It includes nearly 50 clinical research institutions and a central unit for administrative, research, laboratory, biostatistical, and data management functions. Recent scientific advances include the discovery that the insulin-degrading enzyme (IDE) mediates varicella-zoster virus (VZV) infection and cell-to-cell spread. The structure of the parainfluenza virus 5 F protein in its prefusion conformation has been elucidated, revealing the mechanism of membrane fusion. A humanized monoclonal antibody, HV-E16, has shown therapeutic potential against West Nile virus (WNV). A small clinical trial of an experimental WNV vaccine was initiated in 2005.The National Institute of Allergy and Infectious Diseases (NIAID) supports a wide range of basic and applied research in virology to enhance understanding of viral biology, pathogenesis, and immunology, aiming to prevent, control, and treat viral diseases. Research areas include the viral replication cycle, viral structure and function, host-virus interactions, viral genetics and evolution, viral interference, virus vector relationships, epidemiology, and preclinical and clinical research for vaccines, adjuvants, therapeutics, and diagnostics. NIAID also prioritizes research on the emergence of new epidemic viruses through host switching. The NIAID Antiviral Testing Program evaluates the efficacy and toxicity of new antiviral agents using in vitro assays and in vivo animal models. It focuses on identifying antiviral agents for public health important infections, including newly emerging ones. The program includes various viruses and models, such as herpesviruses, respiratory viruses, papillomaviruses, and biodefense viruses. Animal models include HCV, herpesviruses, respiratory viruses, hepatitis viruses, papillomaviruses, and biodefense viruses. The Collaborative Antiviral Study Group (CASG) is a multi-institutional network funded by NIAID to conduct clinical trials and evaluate experimental therapies for viral infections. It includes nearly 50 clinical research institutions and a central unit for administrative, research, laboratory, biostatistical, and data management functions. Recent scientific advances include the discovery that the insulin-degrading enzyme (IDE) mediates varicella-zoster virus (VZV) infection and cell-to-cell spread. The structure of the parainfluenza virus 5 F protein in its prefusion conformation has been elucidated, revealing the mechanism of membrane fusion. A humanized monoclonal antibody, HV-E16, has shown therapeutic potential against West Nile virus (WNV). A small clinical trial of an experimental WNV vaccine was initiated in 2005.