Cover picture: Schematic models for HIV mature and immature states demonstrating the dramatic internal morphological changes associated with maturation. In the immature form, a thick protein shell (~25 nm) composed of Gag is observed beneath the membrane. Viral maturation is induced by the proteolytic processing of Gag into three major structural domains: MA, CA, and NC (colored in blue, red, and green, respectively). The mature HIV particle has a thin protein shell (~5 nm) composed of MA and a conical core. Trimers of the viral envelope protein (colored in brown), which mediate binding to target cells and membrane fusion, are localized on the virus surface. See the article by Kol et al. on page 1777.