Arguments are presented for believing that δ Sct stars and classical Cepheids belong to the same family and obey the same period-luminosity (P-L), period-luminosity-color (P-L-C), and the period-radius (P-R) relations. Existing data for δ Sct stars and for classical Cepheids are used to establish P-L and P-R relations that have internal precisions three-five times better than previous versions