Pre-processing is nothing without scattering. If your spectra are from good aqueous solutions with only fully dissolved particles, there is no light scattering, and as such, pre-processing is not necessary. However, and this is important, scatter could also be defined as unwanted variation in your data with a different source than light scatter. Sometimes it is possible to remove these unwanted variations from your data through pre-processing methods designed to remove scatter. In this paper I would like to take you into my world of pre-processing. Through three different examples I will discuss and tell what kind of information the pre-processing can tell the user about the data, as well as some common pitfalls.