Pottery from archaeological research in lowland Mesopotamia and the adjacent highlands of western Iran provides the earliest clear documentation of regular interaction between the two regions. Analysis of ware distributions and multidimensional scaling of the relative frequencies of painted motifs from sites in the Mahidasht, Kangavar, and several other Zagros valleys in western Iran and from a number of contemporary 'Ubaid and Susa A sites in lowland Iraq and southwestern Iran demonstrate ceramic connections of variable strength between these areas during the Chalcolithic era (ca. 5500- 3400 B.C.). Interpretation using anthropological and human- geographical models suggests that considerable cultural and economic interaction developed between the lowland and highland regions of Greater Mesopotamia in this formative period just prior to the rise of the first cities and states in the lowlands.