The depth resolution function describes the relation between the measured depth profile and the true in-depth distribution of the composition. In high resolution depth profiling, blurring of the profile often is markedly asymmetric and needs several parameters for its precise description. The depth resolution function can be experimentally determined with appropriate reference materials, e.g., samples containing delta layers or sharp interfaces between two media, and it can be theoretically predicted. Recently, a semi-empirical model was developed based on the most fundamental physical mechanisms of atomic mixing, surface roughness, and information depth. These three parameters precisely describe the resolution function that was tested using results obtained on several structures and with different methods, e.g., Auger electron spectroscopy profiles of GaAs/AlAs multilayer interfaces, and secondary ion mass spectroscopy profiles of B delta layers in Si and of SiO2/Ta2O5 multilayers. It is shown how the depth resolution function is applied to reconstruct in-depth distributions of the composition of the measured profiles. Furthermore, information about thin layer thickness, roughness development, and graded composition at interfaces are readily obtained.