The response of cloud systems to their environment is an important link in a chain of processes responsible for monsoons, the Mei-Yu frontal depression, El Nino-Southern Oscillation (ENSO) episodes and other climate variations (e.g., 30-60 day intra-seasonal oscillations). Numerical models of cloud properties provide essential insights into the interactions of clouds with each other, with their surroundings, and with land and ocean surfaces. Significant advances are currently being made in the modeling of rainfall and rain-related cloud processes (e.g., latent heat release), ranging in scales from the very small up to the simulation of an extensive population of raining cumulus clouds in a tropical- or mid latitude-storm environment. Cloud models can also be used to convert the radiances received by cloud-observing microwave radiometers into rainfall rates. Remote sensing of cloud-top properties by high-flying aircraft bearing microwave and other instruments is now beginning to provide powerful tests of these models, particularly when these observations are augmented by simultaneous ground-based radar measurements.