Abstract: An adaptable closure for drinking containers is disclosed. The closure generally includes a concave disk having a central portion and a wide, angled flange. The flange extends upwardly and outwardly from the central portion around the periphery of the central portion. The flange has an upper surface and a lower surface and is flexible and resilient. The lower surface of the flange has the shape of an inverted frustum of a cone for sealingly engaging the inside surfaces of the drinking container. The closure includes a drinking hole offset from the center of the disk and a vent hole also offset from the center of the disk approximately opposite the drinking hole. Finger tabs are provided on the top of the disk to aid in removal of the closure from the drinking container.