Bend me, shape me: Clathrin in action Endocytic clathrin-coated pits were among the first cellular structures described by electron microscopy over five decades ago. Despite this, the question remains: Does clathrin bind to the membrane as a flat lattice and then bend during coated pit invagination, or does clathrin assemble with a defined curvature as membranes invaginate? Avinoam et al. applied two state-of-the-art imaging approaches to resolve this conflict. They suggest that clathrin assembles into a defined flat lattice early in endocytosis, which predetermines the size of the vesicle. The assembled clathrin coat then rearranges through dynamic exchange of clathrin with the cytosolic pool to wrap around the forming vesicle. Science , this issue p. 1369