This study examines decision making concerning tool use and rawmaterial choice through the analysis of bone technology from five sites from the MiddleMissouri subarea of the Northern Plains of North America. The research methods employed include high power optical microwear analysis, experimental replication,and the study of modern bone tool use. At the time of contact with Europeans andEuroamericans, the Mandan, Hidatsa, and Arikara lived in semi sedentary villages along the Missouri River where they practiced a mixed economy centered on both agriculture and bison hunting. The villagers were central in indigenous trade networks and later in the international fur trade, as European and Euroamericans traders and explorers sought to insert themselves into the existing networks. Occasional trade goods are found as early as the seventeenth century, increasing through time as more Europeans and Euroamericans entered the area, indicating that the villagers supplied the newcomers with food, horses, and furs in exchange for those goods. They also were impacted by European diseases, increasing violence, and by accompanying changes in many aspects of their society.Post contact technological change is often modeled as a relatively simple unilinear process in which metal tools quickly replaced older technologies. Analysis of modified bone and antler from historic sites indicates the processes were more complicated. Some tool types were quickly replaced, while others persisted, and there was also variation within tool types. Rather than immediately rendering bone technology obsolete, as has been suggested, there was an initial period of experimentation as people used the new metal cutting and chopping tools to modify the older bone technology. Some tools were made by simply shaping the bone with metal rather than stone, but in other cases the new metal tools were used to create bone tools in completely new forms. Both social and functional factors influence tool choices in raw material, form, and use. This study provides a deeper understanding of many processes involved in technological change in the contact period.