The Khorat Plateau is the broad, flat region of northeastern Thailand and lowland central and southern Laos. Cultural developments on the Khorat Plateau during the early historic period, defined as the 6^th‒13^th centuries CE, are best framed within the context of cultural activities in the Chao Phraya and Lower Mekong Basins, as the Khorat Plateau is land-locked. There is debate regarding ancient populations on the Khorat Plateau, and what political and cultural interactions they had with urban centers in the Chao Phraya and Lower Mekong Basins. Colonial scholars reconstructed cultural chronologies for Southeast Asia, with dominant cultures from the first millennium being Angkor and Dvāravatī. The Khorat Plateau was regarded as less-developed, with certain areas being integrated into Dvāravatī and Angkor. In my view, the evidence available at present does not support this perspective as the best explanation of the region’s past. Archaeological excavations during the second half of the twentieth century revealed the Khorat Plateau to be inhabited by populations with complex social structures since prehistoric times; nevertheless, earlier proposals have gone generally uncontested. My analysis of script styles and artifact typology over a period of centuries supports the suggestion that population centers on the Khorat Plateau consisted of one or more cultural groups distinct from those commonly labelled Dvāravatī and Angkor. The Khorat Plateau was arguably a distinct region in which various societies participated in networks of contact and exchange both across the plateau and with other populations throughout the mainland region and beyond.