As the linear expenditure system (LES) is a popular choice for the consumer demand parts of CGE models, this chapter starts with an extensive analysis of its properties and implementation with cross-sectional data from a household expenditure survey. This includes a discussion of the value of a key feature of LES, the “Frisch parameter”, the income elasticity of the marginal utility of income, and the advantages for allowing for heterogeneous consumers within an LES framework. Then follows details of the econometric application of LES, and the constant elasticity of substitution model for input demands and for substitution between foreign and domestically produced varieties of the same basic good. The resulting estimates are embedded in and CGE model of the Australian economy and reveal the important role played by the values of the demand parameters—for consumers, producers, and the foreign-domestic split.