EARLINET (European Aerosol Research Lidar Network to Establish an Aerosol Climatology) is a joint project of 19 lidar groups operating aerosol lidar systems at 21 stations over a large part of Europe, plus one group focussing on mathematical problems associated with the retrieval of aerosol properties from lidar observations. The main goal of EARLINET is to establish a comprehensive statistically representative data set of the aerosol vertical distribution. For this purpose, each lidar group performs vertical aerosol soundings on a routine basis three times a week on preselected days and times. Additionally several special measurements (e.g. on Saharan dust, temporal cycles, rural and urban differences, long and medium range transport) are part of the project.