The heterogeneous formation of ice crystals is one of the least understood processes in atmospheric research. Within this project the full potential of the synergistic use of radar and lidar instruments with Doppler and polarization capabilities regarding the ice formation in mixed-phase clouds shall be explored. The work involves theoretical and experimental research. The applied instrumentation is part of the Leipzig Aerosol and Cloud Remote Observations System (LACROS) and comprises a 35-GHz cloud radar with scanning, Doppler, and polarization capabilities, a 2-µm scanning Doppler lidar, a 3-wavelength Raman depolarization lidar, a microwave radiometer, and other supporting instruments. Long-term combined observations at the Leipzig site as well as field experiments are performed in the frame of the project. New synergistic algorithms shall be developed in order to identify and quantify the presence of ice and super-cooled liquid water in mixed-phase clouds and the relation between ice formation and atmospheric turbulence. The algorithm development will require the quantitative description of polarization-dependent scattering of electromagnetic waves by ice crystals and water droplets at radar and lidar wavelengths.