Abstract : Realistic rendering of clouds involves solving the complex interaction of light within the cloud and with its environment. Interactive methods achieve efficient cloud rendering by ignoring several lighting effects. However, these effects are visually important, and removing them strongly reduces realism. We present a novel approach for capturing the important effects of multiple anisotropic Mie scattering within cloud layers (i.e., stratiform clouds), and the inter-reflections between the ground and the cloud base under sun and sky illumination. Our model maps well to graphics hardware, enabling the real-time rendering of animated cloud skies over landscapes.