Zika virus (ZIKV), a mosquito-borne flavivirus, was first isolated from a sentinel rhesus macaque in Uganda and soon thereafter from arboreal Aedes africanus mosquitoes. Although only 14 human infections were documented before 2007, human serosurveys in African and Asia suggested widespread exposure. Following 60 years of relative obscurity, ZIKV emerged in Yap, a small Micronesian Island, to cause just over 100 confirmed and suspected cases of febrile illness accompanied by rash and arthralgia, and epidemiologic studies suggested that up to 73% of the human population was infected. A few years, larger outbreaks began in French Polynesia and other islands in the South Pacific, with an estimated tens-of-thousands of infections and an association of some with Guillain– Barré syndrome (GBS), whose incidence increased 20-fold coincident with the ZIKV outbreak. Then, probably in late 2013, ZIKAV reached Brazil, resulting in 2015 in an explosive outbreak involving over one million estimated cases, presumably transmitted by the peridomestic mosquito A. aegypti and possibly also the invasive species A. albopictus. Sexual transmission has also been detected in travelers returning to non-endemic regions. In the Americas, Zika virus Infections were again associated with GBS but also with over 1400 confirmed cases of fetal microcephaly coincident in time and space with ZIKV circulation. Subsequently, the virus has spread to the majority of countries in Latin America and the Caribbean, and microcephaly has also appeared in several of these. Here, I review the current situation of ZIKV in the Americas, potential explanations for its sudden and unexpected emergence, and epidemiologic and basic research needed to test these hypotheses to understand these the dramatic spread, predict future trends, and develop control measures as well as products to protect against severe outcomes of infection. I will also review efforts of the GVN Zika Task force to facilitate collaborative research and educate the public about this emerging virus.