Viruses have complex molecular architectures and have evolved to be ubiquitous parasites of all life forms. They consist of a genome enclosed in a protein or a proteolipid shell. In the 1950s, Watson and Crick as well as Caspar and Klug postulated the basic principles of virus structure organization. The last six decades have seen an exponential increase in the number of virus structures determined to near-atomic resolution using X-ray crystallography and, more recently, cryo-electron microscopy. Here, we review the current knowledge of virus structure and discuss the impact of these structures to gain insight into the life cycle of viruses and the development of anti-viral therapeutics.