EARLINET will establish a quantitative comprehensive statistical database of the horizontal, vertical, and temporal distribution of aerosols on a continental scale. The goal is to provide aerosol data with unbiased sampling, for important selected processes, and air-mass history, together with comprehensive analyses of these data. The objectives will be reached by implementing a network of 21 stations distributed over most of Europe, using advanced quantitative laser remote sensing to directly measure the vertical distribution of aerosols, supported by a suite of more conventional observations. Special care will be taken to assure data quality, including intercomparisons at instrument and evaluation levels. A major part of the measurements will be performed according to a fixed schedule to provide an unbiased statistically significant data set. Additional measurements will be performed to specifically address important processes that are localised either in space or time. Back-trajectories derived from operational weather prediction models will be used to characterise the history of the observed air parcels, accounting explicitly for the vertical distribution.