Publisher Summary This chapter focuses on the phyllosphere, that is, the above-ground surfaces of the plant including stems and trunks. The phyllosphere food web has not been studied extensively, and thus some functions are hypothesized on the basis of what occurs in the rhizosphere, that is, the root-associated surfaces of the plant. The chapter summarizes rhizosphere food web structure and function. The species composition of each organism group in the phyllosphere will be different from that in the rhizosphere, although different taxonomic groups may perform similar functions. The remaining chapter does not further comsider the process of immigration/emigration, but is clearly of great importance in determining which organisms establish and survive on plant surfaces. The balancing between immobilization and mineralization of nutrients improves for plants as food web complexity, and therefore ecosystem productivity, increases. Primary producers, such as lichens, algae, mosses, and cyanobacteria, use the stems and trunks of higher plants as support surfaces, which provide surfaces where these smaller producers obtain light, carbon, and other abiotic resources while escaping competing organisms or predators. Representatives of all functional groups most likely exist on all plants, but the abundance, distribution, and activity of the specific species in these communities or groups are probably markedly different. Bark beetles are found throughout the world in relation with numerous types of woody plants. The activities of the bark beetle may be confined to dead wood, living wood, or even living petioles.