This world encompasses an enormous diversity of environments, and farming systems have evolved to fit into many of them. Rainfed farming systems are found in areas as diverse as the Sahelian zone of west and central Africa; eastern and southern Africa; west and central Asia; Afghanistan and Pakistan; central India; western China; semi-arid Australia; northern Mexico; and the prairies and central plains of USA and Canada. This chapter discusses ways of classifying rainfed farming systems for comparative, predictive and management purposes, and to assist in change from one type of system to another. Here, four categories of rainfed farming systems are distinguished: high-latitude rainfed systems with cold winters; mid-latitude rainfed systems with mild winters; subtropical and tropical rainfed highland farm systems; and semi-arid tropical and subtropical farming systems. Within these categories, systems are subdivided into two archetypes, based on low or high levels of productivity and farming intensity. Factors that influence the intensity and productivity of rainfed farming systems include the ratio of precipitation to potential evapotranspiration, water availability, drought risk, temperature regimes, soil quality, external input use, marketing margins, market access, tenure security, policy environment, and the purpose of crop–livestock integration. There are many interrelationships among these factors. For example, drought risk and water availability are affected by water harvesting practices, risk management practices, soil characteristics, and rainfall patterns and other climate variables. Soil characteristics are influenced by organic and inorganic fertiliser management and enterprise selection (including crop selection and crop–livestock integration). These are affected by input and product prices which in their turn are influenced by marketing margins and market access. Finally, all systems are affected by the quality of market infrastructure, and policies and institutional arrangements.