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 diseases, leading to their prevention, control, and treatment. Key areas of research include the viral replication cycle, viral components, host-virus interactions, viral genetics, interference particles, vector relationships, epidemiology, and preclinical and clinical development of vaccines, therapeutics, and diagnostics. A significant focus is 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. This program aims to identify agents for treating public health threats, including emerging infections. The program covers a broad array of viruses, including herpesviruses, respiratory viruses, papillomaviruses, BK virus, and biodefense viruses. Animal models used include the HCV-SCID/bg/upA chimeric model. 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 comprises nearly 50 clinical research institutions and a central unit for administrative, research, laboratory, biostatistical, and data management support. CASG allows researchers to respond quickly to promising new therapies and emerging clinical priorities. Recent scientific advances in virology are also discussed, highlighting significant progress in understanding and managing viral diseases.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 diseases, leading to their prevention, control, and treatment. Key areas of research include the viral replication cycle, viral components, host-virus interactions, viral genetics, interference particles, vector relationships, epidemiology, and preclinical and clinical development of vaccines, therapeutics, and diagnostics. A significant focus is 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. This program aims to identify agents for treating public health threats, including emerging infections. The program covers a broad array of viruses, including herpesviruses, respiratory viruses, papillomaviruses, BK virus, and biodefense viruses. Animal models used include the HCV-SCID/bg/upA chimeric model. 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 comprises nearly 50 clinical research institutions and a central unit for administrative, research, laboratory, biostatistical, and data management support. CASG allows researchers to respond quickly to promising new therapies and emerging clinical priorities. Recent scientific advances in virology are also discussed, highlighting significant progress in understanding and managing viral diseases.