How has the diversity of plant-insect interactions has developed over deep time? Vascular plants and phytophagous insects together constitute about half of all described species, and their interactions are a dominant feature of terrestrial ecosystems. I would like to know the degree to which patterns of diversity, host plant specificity, and geographic distribution of insect herbivory can be detected in the fossil record, especially the extent to which such patterns have been altered by past extinction events and environmental change. I analyze insect damage on fossil leaves, one of the richest sources of evidence available on species interactions of any kind in the distant past. My dissertation is an evolving and expanding study on Late Cretaceous (~75 million years ago) leaves of western North America, which is a pivotal time during the radiation and diversification of angiosperms (flowering plants).