Coated vesicles concentrate and package cargo molecules to mediate their efficient transport between intracellular compartments. Cytosolic coat proteins such as clathrin and adaptor complexes and coat protein complex I (COPI) and COPII self-assemble to deform the membrane and interact directly with cargo molecules to capture them in nascent buds. The guanosine triphosphatases (GTPases) Arf, Sar1, and dynamin are core components of the coated vesicle machinery. These GTPases, which associate with and dissociate from donor membranes in a guanosine triphosphate-dependent manner, can also actively remodel membranes. Recent evidence suggests that, although structurally diverse, Arf family GTPases and dynamin may play mechanistically similar roles as fidelity monitors that govern cargo packaging and coated vesicle maturation and as components of the fission machinery to mediate vesicle release.