Computable general equilibrium (CGE) models analyse the detailed workings of the whole economy and are widely used in policy research. Typically, a large number of elasticities are needed for the implementation of CGE models, for household demands, for input demands of firms, and for the split between foreign and domestically produced goods. This chapter discusses these matters, emphasising procedures to estimate the demand elasticities and their importance in influencing CGE simulation results. As equilibrium displacement models (EDM) of a single market, or a set of closely related ones, can be interpreted as a special case of the CGE approach, much of the chapter is also applicable to those models.