In order to ensure product and patient safety, impurities and cross-contamination must be excluded during the manufacture of pharmaceutical drugs and active ingredients. For this purpose, it is necessary to establish appropriate validated cleaning procedures for the removal of undesirable impurities and to prove this in the course of cleaning validation using various analytical methods. The lecture will present the basics of cleaning validation and the legal background. The various sampling options will also be discussed. In addition, various active ingredient-specific and non-specific analysis methods will be presented and possible analytical challenges will be highlighted.