This chapter begins by providing a brief overview of the soil biota, including bacteria, fungi, protozoa, nematodes, enchytraeids (Oligochaeta), microarthropods, millipedes, centipedes and earthworms, and their interactions within the soil food web, which refers to the community of organisms (plants, microbes and animals) that live in the soil and are dependent on each other for sources of carbon and energy. It then considers the nematode community, and the manner in which various groups of nematodes interact with each other, and with the rest of the soil biological community. The chapter concludes by outlining the various groups of nematodes that feed on plants and considers the factors that make some of them important pests.