Welcome to this on-demand MOOC “In the footsteps of Zika… approaching the unknown”. This MOOC has been produced by Université de Genève (www.unige.ch), Institut Pasteur (www.pasteur.fr), Université Paris Descartes (www.parisdescartes.fr) and Centre Virchow-Villermé (virchowvillerme.eu). With the help of the intervention of faculty members and international experts, we will explore together the recent Zika phenomenon, a previously rare benign virus that recently turned unexpectedly into the limelight when on the 1st of February 2016 it was declared by the WHO as a Public Health Emergency of International Concern. As this outbreak is still ongoing and under close investigation, this MOOC has the opportunity to be an open learning experience that will follow the marked developments and new discoveries over time. This MOOC will bring you to the heart of the Zika outbreak and invite you to this adventure in uncharted territories. Moreover, we invite you to join the interactive dialogue among participants and facilitators through a community of practice, which promotes questions, critical thinking, participatory learning, as well as interrelated and ongoing collaborative information. Let us learn hand in hand all together to go further in finding clues and eventually solutions! Course description This interdisciplinary course is divided into 8 modules available in 4 languages (subtitles in English, French, Portuguese, Spanish). Each module is organized around a central topic that will help those who take the course to develop their skills and knowledge. Each module provides - interviews with specialists - quizes - recommended readings - online videos and web links. This MOOC will cover a range of topics, such as epidemiology, historical and geographical dispersion of the virus and its vectors through globalization and climate change, its modes of transmission, but also the symptoms, diagnosis and treatment. The different types of preventive measures will be also covered. A special module will focus on possible neurological adverse effects such as the risk for birth defects (microcephaly) in pregnant women, while another one will examine the peripheral nerve paralysis called the Guillain-Barré syndrome. The fact that Zika presents a significant threat to political and economic stabilities and thus reinforces social inequity through South America will be addressed. The revolution in cultural, religious, and legal norms in front of the expansion of Zika will be also debated. Finally, the last two modules will state the role, recommendations and response measures of policy makers and public health organizations under the light of medias.