The literature relating to the impact of other pests on weeds of agroecosystems is minimal. A great deal of literature discusses the effect of organisms used for biological control of weeds; however, pest organisms used as biological control agents are not the subject of this paper. The objective of this review is to present what is known about the impact of insect, pathogen, and nematode pests on weeds; to outline some of the gaps in our knowledge; to present concepts from the ecological literature that might provide insight; and to discuss implications for integrated pest management. The limited data that are available suggest that weeds require fewer resources to survive in the presence of the pest complex than the crop and that weeds would potentially have a greater ability to survive, compete, and reproduce in a competitive environment compared to the planted crop. We suggest that three categories of weed response to polyphagous crop pests may occur in agricultural fields: susceptible weed species or biotypes that host the pest with severe effects on growth and fecundity and therefore are of limited concern in terms of competition for resources; tolerant weed species that host the pest without severe effects on growth and fecundity, resulting in effective competition with the crop and larger pest populations; and resistant weed species that do not host the pest but compete effectively with the crop. We propose the hypothesis that the weed community in many agricultural fields is dominated by plant species that are tolerant or resistant to the endemic pest complex, particularly the soil pest complex, because of constant selection pressure from these pests.