Plant communities vary tremendously in terms of productivity, species diversity, and genetic diversity within species. This vegetation heterogeneity can impact both the likelihood and strength of interactions between plants and insect herbivores. Because altering plant?herbivore interactions will likely impact the fitness of both partners, these ecological effects also have evolutionary consequences. We review several hypothesized and well?documented mechanisms whereby variation in the plant community alters the plant?herbivore interaction, discuss potential evolutionary outcomes of each of these ecological effects, and conclude by highlighting several avenues for future research. The underlying theme of this review is that the neighborhood of plants is an important determinant of insect attack, and this results in feedback effects on the plant community. Because plants exert selection on herbivore traits and, reciprocally, herbivores exert selection on plant?defense traits, variation in the plant community likely contributes to spatial and temporal variation in both plant and insect traits, which could influence macroevolutionary patterns.