Publisher Summary This chapter discusses crop entomology. The starting point of such studies is a correct identification of the insect species, in accordance with the science known as biosystematics. Biosystematics offers a blueprint to follow when dealing with a new pest. For example, the genus Cerotoma (Coleoptera: Chrysomelidae) contains 10 to 12 species distributed from southern Brazil to the northeastern United States. But the knowledge of the name of a species is not an indication of its true potential economic impact or pest status. A next important phase in agricultural entomology is, therefore, the assessment of benefits or losses caused by that species. To assess crop losses and attribute the losses to a specific cause (e.g., the attack of a pest) require setting up experiments to isolate the effect of the pest from all other constraints. Methodologies vary with pest category–—whether the pests are insects, vertebrates, plant pathogens, or weeds. Once the identity and pest status of a species have been well established, it becomes essential to extend the informational base on the life history and habits of the species to the conditions under which the crop is grown. This information is used in modeling the phenology of the pest. The relationship between the phenology of the crop and the phenologies of its various pests is of interest in agricultural entomology.