A system of procedures, methods and analyses have been developed to assess the intensity and diversity of plant–insect interactions in fossil floras based on recording functional feeding groups (FFGs) and damage types (DTs) inflicted on vascular plant taxa by insects, fungi and other organisms. A DT is a distinctive, diagnosable type of damage on live plant tissue that repeatedly is recognizable on plant hosts. DTs are grouped into more encompassing categories of FFGs, of which each FFG represents a distinctive feeding mode, such as skeleltonization, piercing-and-sucking or leaf mining. Units of analyses can be a bulk flora preserved as a fossil deposit, or multiple such floras representing a time series, or successive plant taxa occurring through time as a lineage of related plants or a group with a common ecomorphically interesting feature. Alternatively, FFGs and especially DTs are often the unit of analysis. DTs have been used to evaluate the fate of host-specialized versus host-generalized DTs before and after a major extinction event, such as the end-Cretaceous extinction. Other studies have revealed the effects of major environmental events, as the Paleocene–Eocene Thermal Maximum, or consequences of a major ecological-evolutionary event, the rapid diversification of Early Cretaceous angiosperms.