Long known as a coat system that generates small transport vesicles from the endoplasmic reticulum (ER), the COPII coat also drives ER export of cargo proteins that are too large to be contained within these canonical carriers. With crystal and cryo-EM structures giving an atomic level view of coat architecture, current advances in the field have focused on understanding how the coat adapts to the different geometries of the underlying cargo. Combined with a growing appreciation for the specific roles of individual COPII paralogs in diverse aspects of mammalian physiology, the field is poised to understand how coat assembly and post-translational modification permits structural rigidity but geometric flexibility to handle the diverse cargoes that exit the ER.