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<div>Aerial plant surfaces often support large population sizes (> 10⁶ cells/cm²) of a variety of bacterial colonists. The large majority of these colonists occur in relatively large cellular assemblages, apparently driven by localized abundance of limiting carbon resources and more conducive environmental conditions at such sites. Bacterial growth and survival is strongly favored in cellular aggregates, which also are sites of preferential recruitment of immigrant inoculum. Emigration of bacteria from plants is quite efficient and thus the abundance and composition of microbes in air near plants is strongly influenced by the amount and type of vegetation nearby. While some host plant species selection for particular epiphytic bacterial colonists occurs, phyllosphere microbial communities appear to be assembled from a metacommunity contributed and shared by nearby plants in a process that likely involves microhabitat modification at sites of microbial aggregation by initial plant colonists. The selection appears to occur from bacterial strains adapted for life on foliar plant surfaces rather than from other habitats. Leaf surface microbial communities therefore are quite context-dependent and can be managed either by direct inoculation or by changing the agroecological context in which crops are grown.</div>