The Constant Elasticity of Substitution (CES) function is popular in several areas of economics, but it is rather rarely used in econometric analysis because it cannot be estimated by standard linear regression techniques. This chapter starts with a discussion of several approaches for estimating the traditional CES function with two inputs as well as nested CES functions with three and four inputs. It proceeds with the demonstration of how these approaches can be applied in R using the add-on package micEconCES and describes how the various estimation approaches are implemented in the micEconCES package. The chapter concludes with an illustration of the usage of this package by replicating some estimations of CES functions that are reported in the literature.