For a virus to invade a host cell it needs to penetrate the physical barrier imposed
by the plasma membrane. Viruses have evolved specialized surface proteins to meet
this challenge. These proteins facilitate delivery of the viral genetic information into
the host cell by either fusing the viral envelope with a host cell membrane (enveloped
viruses) or by forming membrane pores (non-enveloped viruses). Membrane fusion and
pore formation critically depend on the engagement of host cell receptors and receptor
choice is a key determinant of viral tropism. The multi-faceted interplay between viral
and cellular factors during virus entry is a fascinating field of study, which can provide
important insight into viral pathogenesis and define new targets for intervention. This
book provides a comprehensive overview of this exciting field of research.