Plant-feeding, or plant-parasitic, nematodes are ubiquitous in soils that support plant growth, and at least one species is usually present in association with the roots or shoots of maize. However, the macro-effects of phytophagous nematodes are notoriously difficult to test and measure, and depend upon many factors associated with the plant, its environment, and the nematodes themselves. This chapter begins with an introduction to soil and plant nematodes, covering their general characteristics, identification and an overview of our current knowledge of their effects on maize. Subsequent sections review various types of nematodes, with particular focus on those which are highly likely to cause yield losses and other damage to maize crops such as lesion, root-knot and vermiform nematodes.