The sources of gypsum, used as an interior building material in the Bronze Age palaces of Crete, some buildings at Akrotiri in Thera and in the mainland palaces at Mycenae and Tiryns, have been attributed by archaeologists to geological deposits in Crete itself, on mainland Greece, or in the Ionian islands of Zakynthos and Kephallenia. Isotopic analyses of sulfur and strontium have been used to characterize the Greek gypsum deposits and to investigate the provenance of gypsum excavated at Knossos, Hagia Triadha, Akrotiri, Mycenae and Tiryns. These analyses show that central Cretan gypsum deposits of Pliocene age supplied the Minoan palaces, Akrotiri on Thera and the palace of Mycenae. In contrast, Tiryns obtained its gypsum from Triassic gypsum deposits, either on Crete or in the Ionian islands or on mainland Greece. -- AATA