Characteristics of low clouds and of warm-rain production are investigated in terms of droplet growth, based on the effective droplet radii retrieved by a combined use of visible, infrared, and microwave satellite remote sensing. We have developed a retrieval algorithm to derive the cloud physical properties from the Tropical Rainfall Measuring Mission (TRMM) satellite data. We propose to categorize low clouds into the following three groups: (1) non-drizzling, non-raining clouds, (2) non-raining clouds with drizzling near the cloud top, and (3) raining clouds, in terms of the effective radii derived by two different schemes. This categorization is supported by examination of the correlation between static stability and the retrieved results in the three ``precipitating regions'' (the Middle Pacific, SPCZ, and ITCZ cumulus regions) and in the four ``nonprecipitating regions'' (the Californian, Peruvian, Namibian, and eastern Asian stratus regions). The rain rate derived by Precipitation Radar (PR) provides global characteristics consistent with our results. Californian and Peruvian stratus clouds are found to frequently have the drizzle mode near the cloud top, whereas Namibian strati have fewer chances to drizzle. The drizzle mode almost completely disappears in the eastern Asian region in winter. The cloud-aerosol interaction is a promising candidate for suppressing formation of the drizzle mode in nonprecipitating clouds.