This document provides guidance for the use of charge conditioners for aerosol particles, especially for particle characterization and for the generation of calibration and test aerosols. It provides a methodology to specify the performance of charge conditioners and for adequate quality control with respect to their application in particle size and concentration measurement with differential mobility analysing systems (DMAS) and in particle size classification with differential electrical mobility classifiers (DEMC). For these applications, this document covers particle charge conditioning for particle sizes ranging from approximately 1 nm to 1 µm and for particle number concentrations at the inlet of the charge conditioner up to approximately 107 cm-3. This document does not address specific charge conditioner designs or other applications besides those mentioned above. Radiation safety for charge conditioners with radioactive sources or x-ray tubes is not covered by this document, since regional, national and international regulations and laws apply.