Viruses undergo dramatic structural reorganizations at many critical stages of their life cycles, including during host cell invasion, genome expulsion, assembly, and cell egress. The changes often involve concerted changes among hundreds of protein components and, in the case of enveloped viruses, membranes as well. From this perspective, virions are intricate, nano-scale cell-invasion and replication machines. The dynamic structural transitions are attractive targets for anti-viral therapeutics that would "throw a spanner into the works" and arrest viral infections. We use a suite of biophysical, structural, and biochemical techniques including X-ray scattering, cryo-electron microscopy, and fluorescence microscopy to understand the function of viral machinery. The viruses we study include influenza A virus, hepatitis B virus, and dsDNA bacteriophages.