The chemical ATP, adenosine triphosphate, is the fuel that powers all life. Despite ATP's central role, the structure of the enzyme generating ATP, F1Fo-ATP synthase, in mammals, including humans, has not been known so far. Now, scientists report the first complete structure of the mammalian F1Fo-ATP synthase. This structure also settles a debate on how the permeability transition pore, a structure involved in cell death, cancer, and heart attacks, forms.