We study molecular evolution at the host-virus interface, where specific protein-protein interactions drive rapid evolution of viral surface proteins, the host receptors that they bind, and the antibodies that inhibit these interactions. We leverage a combination of evolutionary, biochemical, and virological approaches to connect the functional effects of amino acid mutations to their biophysical origins and evolutionary consequences. Our basic studies of protein evolution shed light on important phenotypes in virology and immunity, from viral zoonosis to the development of broadly protective antibodies. We are building off current projects on SARS-CoV-2 and HIV to develop a broad research program studying diverse emerging viruses of public health interest.