The physical and chemical properties and processes of clouds are of interest from a variety of perspectives, such as acid deposition, oxidant chemistry, and radiative transfer in the atmosphere. The Kleiner Feldberg Cloud Experiment was conducted in October-November 1990 at the field observatory of Kleiner Feldberg near Frankfurt, Germany, in the Taunus Highlands. The experiment was planned and organized within the EUROTRAC sub-project GCE (Ground-Based Cloud Experiment). The general aim of this project is to experimentally investigate physical and chemical processes occurring in ground-based clouds, to provide the basic information needed to understand the incorporation and transformation of trace atmospheric constituents within the multiphase cloud system. This text reports the results of the Kleiner Feldberg Cloud Experiment, addressing the main scientific questions related to the properties of clouds and the processes taking place in the cloud multiphase system.