In June–July 2009, the Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI) took place at the Cabauw Experimental Site for Atmospheric Research (CESAR) in the Netherlands. More than thirty different in-situ and remote sensing instruments from all over the world have participated. The main objectives of CINDI were to determine the accuracy of state-of-the-art ground-based measurement techniques, both in-situ and remote sensing, for the detection of atmospheric nitrogen dioxide and to investigate their usability in satellite data validation. It is expected to result in recommendations regarding the operation and calibration of such instruments, retrieval settings, and observation strategies for the use in ground-based networks for air quality monitoring and satellite data validation. A large data set of continuous measurements of nitrogen dioxide and other atmospheric constituents has been collected under various meteorological conditions and various air pollution levels. This special issue contains papers that use the CINDI data set.