This week marks 6 months since WHO was notified of an outbreak of Ebola virus disease in Guinea. This outbreak has since evolved into the largest, most severe and most complex outbreak in the history of the disease. The number of cases and deaths far exceeds those from all past outbreaks combined. The 3 most-affected countries – Guinea, Liberia and Sierra Leone – face enormous challenges in stopping transmission and providing care for all patients. This series of essays reflects on the evolution of this unprecedented outbreak – the multiple challenges, small successes and despairing setbacks.