Current knowledge concerning the effects of drought on forest insects and diseases was reviewed and compared between the moderately wet and structurally diverse forests of the eastern United States and the drier forests of the western United States. Evidence suggests a non-linear relationship between drought intensity and outbreaks of aggressive bark beetle species (i.e., those capable of causing extensive levels of tree mortality) in the western United States, where moderate drought reduces bark beetle population performance and subsequent tree mortality and intense drought increases bark beetle performance and tree mortality. There is little evidence for a role of drought in outbreaks of the southern pine beetle in the southeastern United States. Defoliators show no consistent response to drought. Interactions between forest diseases and drought are poorly understood, but available evidence suggest reduced pathogen performance and host impacts for primary pathogens and pathogens whose lifecycle depends directly on moisture (humidity). In contrast, secondary fungal pathogens are likely to have greater performance and host impacts. The scientists published their results in a special issue on drought in Forest Ecology and Management. A related effort explores the role of drought on recent levels of tree mortality in the Sierra Nevada, where some 67 million trees have died.