The cell imposes multiple barriers to virus entry. However, viruses exploit fundamental cellular processes to gain entry to cells and deliver their genetic cargo. Virus entry pathways are largely defined by the interactions between virus particles and their receptors at the cell surface. These interactions determine the mechanisms of virus attachment, uptake, intracellular trafficking, and, ultimately, penetration to the cytosol. Elucidating the complex interplay between viruses and their receptors is necessary for a full understanding of how these remarkable agents invade their cellular hosts.