Summary Fifty significant items from the large body of radiometric data on the Cretaceous period are reviewed and the following dates are acceptedas a basis for discussion: Jurassic-Cretaceous (Volgian-Ryazanian) boundary: 136 m.y.; Lower Cretaceous-Upper Cretaceous (Albian-Cenomanian) boundary: 100 m.y.; Upper Cretaceous-Tertiary (Maestrichtian-Danian) boundary: 64 m.y. A precise scale of geochronology for this period is impeded by inadequate stratigraphical dating of igneous events, unreliability of results from sedimentary sources (glauconite), and lack of international agreement on the limits of the Cretaceous System.