The Food and Agriculture Organization of the United Nations (FAO) and the International Institute for Applied Systems Analysis (IIASA) have cooperated over several decades to develop and implement the Agro-Ecological Zones (AEZ) modelling framework and databases. AEZ relies on well-established land evaluation principles to assess natural resources for finding suitable agricultural land utilization options. It identifies resource limitations and opportunities based on plant eco-physiological characteristics, climatic and edaphic requirements of crops and it uses these to evaluate suitability and production potentials for individual crop types under specific input and management conditions.