This European Standard gives guidelines on the measurement of the fine particle fraction of the aerosol, especially for the determination of the number concentration of ultrafine aerosols and nanoaerosols at workplaces by use of condensation particle counters (CPC).This European Standard deals with the CPC's principle of operation, problems of sampling in the workplace environment, aspects for selecting a suitable instrument, limits of application, use of different working fluids and technologies, calibration, equipment maintenance, measurement uncertainty, and reporting of measurement results. Potential problems and limitations which are of relevance for workplace measurements are described.