The Zika virus (ZIKV), a flavivirus related to yellow fever, dengue, West Nile, and Japanese encephalitis, originated in the Zika forest in Uganda and was discovered in a rhesus monkey in 1947. The disease now has “explosive” pandemic potential, with outbreaks in Africa, Southeast Asia, the Pacific Islands, and the Americas. Since Brazil reported Zika virus in May 2015, infections have occurred in at least 20 countries in the Americas. Puerto Rico reported the first locally transmitted infection in December 2015, but Zika is likely to spread to the United States. The Aedes species mosquito (an aggressive daytime biter) that transmits Zika virus (as well as dengue, chikungunya, and yellow fever) occurs worldwide, posing a high risk for global transmission. Modeling anticipates significant international spread by travelers from Brazil to the rest of the Americas, Europe, and Asia. What steps are required now to shore up preparedness in the Americas and worldwide