The most complex system of writing (using the word in a broad sense) that Andean peoples possessed before the Spanish invasion of 1532 was the cord-and knot-based medium called khipu (Quechua) or quipu (Spanish). The material makeup of khipu is a story of variation over time, with some longue durée continuities. Khipu had a brief, spectacularly productive heyday as the official medium of the Inka state (established some time during the 15 th century ce until 1532 ce). The great majority of all the 600-odd more or less complete khipus held in museums and accessible private collections are catalogued as imperial Inka artifacts, but new radiocarbon results show that some date from the Spanish colony (Cherkinsky and Urton, forthcoming). The Ethnologisches Museum in Berlin and the American Museum of Natural History in New York have the largest collections. Online offerings suggest that an unknown number of them (some fake) are in other hands. Inka khipus were largely standardized in format and material content (Figure 1). But Inkas are not the only principals in this story. The cord medium underwent a long, varied evolution both before and after khipus' brief Inka florescence. Both pre-and post-Inka khipus differed widely from Inka ones in physical substance and form. This chapter consists of a historical and a functional section. In the first half I discuss material attributes of Inka, pre-Inka, and post-Inka khipus, respectively, with emphasis on change. By contrast, in the second half of this chapter I emphasize material continuity: material traits that make a khipu a khipu, and how they affect culture as lived through inscription. For the spatial distribution of the evidence discussed, see the map in Figure 2. Recent Research Historical Variation in Khipu Material Support of Meaning in the Inka Canon Inka-era khipus' physical characteristics as substrate for meaning have been the object of intense study since the 1920s, largely by archaeologists hosted in museums. Inka khipus are How to cite this book chapter: