Sputter depth profiling using AES is a routinely applied method in surface, interface and thin-film analysis. After about 30 years of constant progress the present state is characterized by improved instrumentation, e.g. sample rotation capabilities and low-energy ion guns, as well as by improved quantification methods for the raw data depth profiles. Profile quantification by reconstruction of the original in-depth distribution of composition using the so-called (atomic) mixing-roughness-information depth (MRI) model has proved to be a powerful tool for extracting more precise and extended information of the measured profiles, e.g. quantification with submonolayer accuracy, intrinsic determination of the sputtering rate and determination of localized interdiffusion coefficients as low as 10 −22 m 2 s −1 were obtained. Because the MRI model is based on physically well-defined parameters, it can be applied successfully to other profiling techniques such as SIMS or GDOES. Although in many cases the MRI model can be applied in its original version, some materials require modification by a preferential sputtering coefficient. Further modifications will be necessary to take care of non-linear effects in the concentration dependence and in the compositional distribution within the atomic mixing zone. In summary, quantitative depth profiling using AES has now attained an advanced stage, where its combination with the MRI model is being introduced in commercial instrument software.