The first half of the twentieth century witnessed profound changes in smallholder agriculture in many parts of Africa. There was a rapid spread of exotic staple food crops such as maize, cassava and sweet potatoes. In many cases the adoption of these crops led to increases in productivity as they replaced millets and sorghum. In addition the development of new trade routes opened the way to a remarkable expansion in the production of traditional and exotic export crops. There was also a more limited uptake of introduced technologies such as ox-ploughing. In many cases the move into cash cropping resulted in changes in the farming system. These occurred in situations where the growing of perennial crops or access to markets encouraged people to abandon a truly shifting cultivation for a more static lifestyle. A striking feature of these developments was the speed at which many of these major innovations were adopted by large numbers of smallholders. This undermined the theory that African smallholders were basically conservative. The changes and production increases of the first part of the century were followed by the static situation of the past forty years. Despite the introduction of fertiliser, new varieties and intensive research and extension efforts there has been little progress in raising yields, preserving soil fertility or maintaining per capita production of food and cash crops. It is these issues which present the major challenges for the coming century.