Atmospheric clouds play important roles in the atmospheric water cycle, atmospheric composition change, the climate system, and the stratospheric ozone loss. They strongly interact with aerosols and trace gases. Physical and chemical processes need to be understood and parameterized to correctly represent clouds in numerical models. In the lower stratosphere solid cloud particles are of essential importance. Particularly, the phase composition is under discussion. This includes the different ways of phase characterization in the field and in lab studies. In the upper troposphere cirrus clouds are affected by the competition of different nucleation mechanisms, i.e. homogeneous versus heterogeneous nucleation comprising the impact of mineral dust, organics, and other aerosols. In tropospheric research, aerosol-cloud interaction, cloud chemistry with special emphasis on organics, and the radiative properties of clouds are currently of particular interest. This session aims at discussing recent results from field measurements, laboratory experiments, and modelling studies. Contributions are welcome from studies related to tropospheric liquid water clouds, mixed-phase clouds, cirrus clouds as well as polar stratospheric clouds (PSCs).