After surveying the development of world-historical views from Herodotus and Ssu-ma Chen to Spengler and Toynbee, the author sketches his own current understanding of the best approach to the subject. The organizing concept is hard to name, being the geographically largest circle of effective interaction among peoples of diverse cultures and circumstances. In recent times interaction has become literally world-wide; but before 1500 several different communications nets co-existed, each with a dynamic of its own, though the largest was always situated in Eurasia and now embraces the globe. Competing terms exist: "interactive zone," "world system," and "ecumene," but none is completely satisfactory or generally accepted by world historians. Nonetheless, the author asserts that a perceptible drift towards recognizing the reality and centrality of this large structure in the human past has begun to show up among practicing world historians; and the balance of the essay sketches how key alterations in patterns of Eurasian communication mark the principal stages in the expansion and intensification of interaction within the Eurasian ecumene.