This is a textbook on insect biology and entomology, which is a branch of zoology and an important subject in Agricultural and Horticultural sciences. Courses in entomology are important courses in several colleges and universities in India and abroad. This textbook is based on the syllabus of undergraduate and postgraduate courses of Entomology prescribed by the Indian Council of Agriculture Research. This textbook covers all contemporary as well as traditional systems of classification and studying of insects. It also contains information on biology of insects. The book is useful for instructors as well as postgraduateand undergraduate students involved in the study of insects.