This chapter provides an overview of insect ecology. Insect ecology is the study of interactions between insects and their environment. The primary challenge for insect ecologists is to place insect ecology in an ecosystem context that represents insect effects on ecosystem properties, as well as the diversity of their adaptations and responses to environmental conditions. Until recently, insect ecologists focused on the evolutionary significance of insect life histories and interactions with other species, especially as pollinators, herbivores, and predators. Research on insects and associated arthropods has been critical to the development of the fundamental principles of ecology, such as evolution of social organization, population dynamics, competition, predator–prey interaction, mutualism, island biogeography, metapopulation ecology, and regulation of ecosystem processes such as primary productivity, nutrient cycling, and succession. Complex systems with feedback mechanisms can be partitioned into component subsystems, which are composed of sub-subsystems. Viewing the ecosystem as a nested hierarchy of subsystems, each with its particular properties and processes, facilitates the understanding of the complexity. Each level of the hierarchy can be studied at an appropriate level of detail, and the properties of each level can be explained by the integration of its subsystems. An important aspect of this functional hierarchy is the “emergence” of properties that are not easily predictable by simply adding the contributions of the constitutive components. Emergent properties include feedback processes at each level of the hierarchy.