A MAP holds the corners M icrotubule-associated proteins (MAPs) reinforce microtubules (MTs). Fourniol et al. provide the fi rst close-up of a MT-bound MAP, clarifying how it adds stability. The building blocks of MTs are dimers of one and one -tubulin subunit. These dimers line up end to end to build protofi laments, which in turn align side by side in a ring shape to form a hollow MT. MAPs he...