Ice and mixed-phase clouds have large impacts on Earth’s climate. Composite analyses of in-situ, remote sensing observations and multi-scale model simulations are needed for understanding their physical properties, radiative effects, and the relative impacts caused by in-cloud processes. We encourage studies that apply model simulations and observations to investigate ice and mixed-phase cloud characteristics and cloud impacts on regional and global climate. Relevant topics include: (1) observationally-based analyses of ice and mixed-phase clouds, in-cloud processes, secondary ice formation, cloud phase distributions from cloud scales to global scale, (2) assessments of ice crystal and liquid droplet microphysical properties, (3) cloud macrophysical characteristics, including spatial heterogeneities and temporal variabilities, (4) sub-grid scale variabilities of relative humidity, water vapor, temperature and vertical velocity in model parameterizations, (5) radiative forcing of ice and mixed-phase clouds from observations, reanalysis data and model simulations, (6) observationally-constrained estimates of climate impacts of ice and mixed-phase clouds.