The Penn-CEIRR brings together a collaborative group of scientists focusing on influenza virus surveillance, epidemiology, immunology, virology, evolutionary biology, clinical studies, and modeling. We have an extensive influenza virus surveillance program that includes sampling in the United States, Hong Kong, Cambodia, the United Kingdom, and Bangladesh. Our Center is completing studies to determine how immune responses to influenza viruses develop across different populations with high and low vaccination risks, and we are identifying immune responses associated with protection versus susceptibility. We are completing a series of human and animal studies to determine how prior influenza virus exposures shape immune responses to new viral strains, and we are developing models to forecast influenza virus evolution and epidemiology based on experimentally measured variations in immune specificities across different populations. We are studying pathogens with pandemic potential, including emerging swine and avian influenza virus strains. Combined, our efforts will fill critical knowledge gaps in influenza virus and other emerging pathogen research, reveal factors underlying viral emergence and transmission, and accelerate development of new and improved control measures.