The global spread of epidemic Zika virus (ZIKV) began in Micronesia in 2007, followed by epidemics in French Polynesia in 2013-14, other South Pacific islands in 2014-15, and the Americas in 2015-16. A dramatic increase in severe congenital malformations (microcephaly) potentially associated with ZIKV in Brazil, combined with the rapid geographical spread, led the World Health Organization to declare ZIKV epidemic a Public Health Emergency of International Concern. Although ZIKV was first isolated nearly 70 years ago, very little is known about the biology, epidemiology and clinical manifestations because transmission has been sporadic and silent for most of that time. Here we review what is and is not known about ZIKV, with emphasis on the gaps in knowledge about ZIKV and the possible inaccurate assumptions made based on what we know about related viruses.