The ruddy flakes of a rusted nail are a sure sign that an undesirable chemical reaction has occurred at the surface. Understanding how molecules and atoms behave with each other, especially at surfaces, is central to managing both desirable chemical reactions, such as catalysis, and undesirable reactions, like a nail’s corrosion. Yet the field of surface chemistry has been challenged for nearly 100 years to develop predictive theories for these reactions. Now there’s progress, thanks to some new approaches.