This report documents the hazardous conditions in which artisanal miners, including thousands of children, mine cobalt in the Democratic Republic of the Congo. It goes on to trace how this cobalt is used to power mobile phones, laptop computers, and other portable electronic devices. Using basic hand tools, miners dig out rocks from tunnels deep underground, and accidents are common. Despite the potentially fatal health effects of prolonged exposure to cobalt, adult and child miners work without even the most basic protective equipment. This report is the first comprehensive account of how cobalt enters the supply chain of many of the world’s leading brands.