Integrated aquaculture-agriculture farming systems are defined as sys tems where the outputs from aquaculture become inputs to agricultural enterprises and vice versa, resulting in a greater total effect than the sum of the individual subsystems. Qualitative models of these systems indicate where wastes and by-products substitute for or supplement external inputs, particularly petroleum-based chemicals. Models stimulate new ideas about where and how new enterprises can be added and what interactions may be exploited. Examples from Bangladesh, Malawi, and Vietnam illustrate this. The qualitative method described in this article shows how bioresource exchanges between aquaculture ponds and the other agricultural enterprises in the farming system can be drawn by farmers. Material flows are defined as the material outputs or by-products and waste of one enterprise that are used as an input for or that flow into another enterprise.