Clathrin-coated vesicles bud from the plasma membrane and from the trans-Golgi network; both populations of coated vesicles participate in the endocytic pathway. Coated-vesicle formation is initiated by the binding of cytosolic adaptor complexes to putative adaptor receptors on the appropriate membrane. Clathrin then binds to the adaptors and assembles to form a coated bud, which pinches off as a coated vesicle. The GTPase dynamin facilitates the formation of coated vesicles at the plasma membrane through an as yet unknown mechanism. Recent studies suggest that regulatory mechanisms may operate at each of these stages.