To be sustainable, food and non-food processing systems must impart value to local production by generating jobs and incomes while managing water- and energy-related environmental constraints. The design of sustainable processes must take into account different forms of organization between actors – from small producers to more industrialized tropical agri-chains –, the scale – artisanal, semi-industrial, etc. – for which they are meant, and the evolution of consumer demands, with these latter often wanting to sustain their traditional diets but with the best possible nutritional and health qualities. The processes must take into account the numerous constraints and criteria pertaining to raw materials, finished products, and the local environment in the countries of the South. Environmental sustainability of processing systems also requires improvements in the energy efficiency of processes, reduction in the use of water (recycling), the deriving of value from co-products, and more effective pollution control. The approach proposed by CIRAD aims to analyze the diversity of existing processing systems, design more innovative and sustainable ones, and then provide them with the necessary support in real-world contexts in association with the other actors of the tropical agri-chains. Food processing systems are complex because they involve various unitary operations that have to conform to demanding specifications. A modelling approach allows the selection of technological solutions to be formalized and rationalized. To incorporate sustainability criteria in the design of food and non-food processing systems, new design processes make use of multi-criteria analysis methods.