Modellers’ choice on closure rules affects CGE model results and consequently its policy prescriptions. In this book the aim is to detect and assess this issue, both through a theoretical discussion and an empirical application. Starting from Amartya Sen’s 1963 paper, literature presents many contributions on this topic. Currently, the closure rule problem is not central in the CGE debate. After a brief introduction on CGEs, their development and their structure, a series of simple maquette is presented. After theory, we move into the real World analyzing through different models (Neoclassical, “Bastard Keynesian”, and Structuralist/ Post- Keynesian), and through different closure rules for macro- aggregates (private, public and foreign savings) the impact of the Regional Trade Agreement of SADC with respect to the Mozambican economy. The analysis is performed using the GAMS/MPSGE software.