Entomology, which literally means the scientific study of insects and their natural world, comprises multiple disciplines, including biology, ecology, agriculture, medicine, and forensic science. Insects are the most diverse and abundant group of animals on earth, and they are essential to the functioning of all ecosystems, through, for instance, processes such as pollination, decomposition, and nutrient cycling. They are a major food source for many species of fish, amphibians, reptiles, birds, and mammals. This chapter aims to provide a fundamental understanding of insect biology, behavior, taxonomy, and their ecological importance. It encompasses insect classification, anatomy, physiology, behavior, ecology, and interactions with the environment, including humans. Knowledge of entomology is crucial in managing both beneficial and detrimental insect populations to promote sustainable agricultural production, biodiversity conservation, and animal health. Entomological knowledge is also critical for understanding the impacts of climate change on insect populations and their interactions with the environment.