The illustration on the cover of the thirty-first edition, the structure of Zika virus protein determined at 3.8 Å resolution, was generously prepared and provided by Lei Sun. The supporting data appeared in: Sirohi D, Chen Z, Sun L, Klose T, Pierson TC, Rossmann MG, Kuhn RJ: “The 3.8 Å resolution cryo-EM structure of Zika virus protein”, Science 2016;352:497-470. Together with the Zika virus, first recovered in the Zika valley of Uganda, the viruses responsible for yellow fever, West Nile fever, and dengue fever are members of the Flavivridae family of positive-strand DNA viruses. The cover illustration indicates the resolving power of cryo-electron microscopy (cryo-EM). More importantly, it recognizes the medical significance of infection by the Zika virus, which in pregnant women can result in a significant risk of congenital microcephaly and associated severe mental impairment. While Zika virus typically is transmitted by the bite of an infected mosquito, emerging evidence suggests that under certain conditions the Zika virus may also be transmitted between human subjects.