Agriculture constitutes the largest economic sector and professional occupation in Chad, and is undergoing rapid changes due to processes of population increase, institutional reforms, conflicts in neighbouring countries, increasingly globalized trade networks, and environmental changes. But despite their importance for livelihoods and economic growth, the specific patterns and drivers of change in the agricultural sector are however poorly understood. This has mostly been a result of low data availability and a lack of comprehensive research programs to address the agricultural changes of various spatial scales. By analysing crop statistics on a level of detail that have not been done before, this thesis has been able to show how the agricultural production is changing over time and between the different administrative regions in Chad. In general it found that the harvested area has been increasing faster than the yield, and that a majority of the changes have happened under abrupt rather than gradual changes. By using this detailed understanding of the patterns of change, and by combining numerous kinds of relevant datasets on hydrology, demographics, international aid, market prices, conflicts, and agricultural practices, this thesis has evaluated potential factors of these changes with an extent and detail that have not been done before. This evaluation have showed that variations in hydrological conditions, market prices, and food security conditions can be linked to the variability in crop production. By looking at descriptions of livelihood conditions in agricultural areas, factors such as material and technical farm support have been linked to abrupt changes in the crop production for specific areas. Also, the differences in long term change between the administrative regions in Chad have been explained by differences in demographic factors and amount of international aid received. These and similar results are relevant to increase the understanding of how agricultural societies evolve in Chad, and how strategies and interventions can be developed to assist local communities in their objectives. More specifically, the results can be used to evaluate the effects of certain events or policies, and to improve seasonal predictions for crop production and food availability. Beyond Chad, the results and methods developed for this thesis are relevant for application in the wider Sahel, where the agro-ecological and institutional conditions share some key characteristics
