A Social Accounting Matrix (SAM) can be interpreted as a complete description of the entire market transactions of commodities and primary factors made by the agents within an economy. A SAM describes also the transfers of revenues between agents (for example, social benefits payed by the government to households). A SAM is founded on the principle of balance between expenses (in columns) and the receipts (in lines) on the level of each account, but also on the level of the whole accounts. In this way a SAM is based on the Walras’ law in which all markets are balanced. The building of a SAM required to compile different statistical data and to reconcile these alternative sources. The SAM is now widely used in economic modeling and in particular in Computable General Equilibrium model. The SAM that we describe in this paper is those used by the GEMINI-E3 model.