The book has been prepared to teach third-year students from the Department of Animal Biology at the Faculty of Science, Tishreen University, and approved accredited laboratories, as it focuses on the causes of insect spread, their classification, and the environment in which these organisms spread. It also explains the most important biotic and abiotic environmental factors that affect insects and the concept of the determinant factor. Therefore, this course shows the different means of defense that it resorts to to defend itself against predators of the environment and provides value and talk about adaptations to environmental conditions.