The biological conditions are specified under which a tree-crop system can give a yield benefit. Models can be used to explore the wide range of options as regards choice of trees and crops, plant density, plant spacing and soil management. Although ample opportunities exist for tree-crop combinations to out yield monocultures of either trees or crops, the conditions under which both the tree and the crop combinations to outyield monocultures of either trees or crops, the conditions under which both the tree and the crop component as much benefit from the mixing are narrow. If in ‘social forestry’ systems the stakeholders (forestry organization and farmers) are exclusively interested in the tree and crop component, respectively, little harmony in management decisions can be expected and strict enforcement of rules is needed, but may not be feasible. If other types of sharing arrangement can be agreed on, a much wider range of locally adapted solutions can be found, which more fully exploit the opportunities of tree crop synergy.