Thousands of plant species are infected by parasitic worms. The cost to world agriculture of nematode parasitism was estimated recently to be US$125 billion annually, although the lack of clear disease symptoms might lead some growers to underestimate yield loss. Integrating several control strategies is often necessary to limit economic losses. Chemical control is restricted by economic constraints, by grower preference, or by government restrictions to limit the environmental harm that nematicides cause. Some plants have unique resistance genes that protect them from certain pests. Several nematode resistance genes in plants have been cloned, and the majority of them resemble other plant resistance genes. Nematode resistance is typically characterized by host plant cell death around or at the endoparasitic worm's feeding site. The timing and location of the resistance response vary depending on the resistance gene and nematode interaction. Although genetic data suggest that single genes in the worm can affect whether a plant produces a resistance response, homologous nematode effectors corresponding to plant resistance genes have yet to be found. Recently, RNA interference (RNAi) in plant parasitic nematodes were demonstrated. It is a potentially powerful investigative technique for genome-wide gene function discovery, which should aid in our understanding of plant parasitic nematodes. RNAi should aid in identifying genes and, thus, protein targets for worm control techniques. Prospects for new resistance are contingent on the plant producing an efficient form of double-stranded RNA in the absence of an endogenous target gene without harming itself. These RNA molecules must subsequently be available to the worm and capable of being ingested through its feeding tube. If these conditions are met, crop resistance may be developed by a plant sending a dsRNA that targets a nematode gene and generates a deadly or severely damaging RNAi effect on the parasite.