This textbook contains important, comprehensive and in-depth account of all aspects of insect physiology, providing wherever necessary also the fundamental knowledge of the various systems. Although it is aimed as a resource material for postgraduate students of entomology, it would serve as an essential reference source for invertebrate physiologists and neurologists, entomologists, zoologists and insect biochemists. To achieve this goal, extensive references have been made to several textbooks and reviews, to a few research papers dealing with applied aspects of insect physiology and the resources available over the net. The first chapter deals with the anatomical and physiological attributes of the integument conferring insect success with a discussion on the use of the chemical properties of the cuticle to design novel molecules to control insect pests. The chapter also indicates that the structural design of the cuticle could itself be applied in the field of material science to develop hard structures which can withstand the harshness of the environment. Chapter two discusses the diversity in growth and life cycle patterns in insects. Chapters three and six deals with the digestive and excretory systems as potential targets for pest management. Aspects of the circulatory system of insects are presented along with an account on the new frontiers in insect immunity in chapter four. This would appraise the reader on the possible improved use of entomopathogens in biological control, in the discovery of antimicrobial molecules that can be exploited by humans, and of new strategies for management of insect vectors of human and animal disease. While the dynamism of the respiratory system (Chapter five) is presented as a key to their success, the use of the knowledge thus gained in fluid dynamics and biomechanical research is mentioned. An up to date account on the insect nervous system is presented in Chapter seven, together with a note on learning, memory and intelligence in insects. Chapter eight deals with the reproductive system of insects while chapter nine deals with hormones and regulation of metabolism, moulting and diapause. General protein, carbohydrate and lipid metabolism and their energetic are presented in chapter ten along with the physiology of regulation in cold hardiness and flight. Chapter eleven deals with muscular coordination while an in depth account on the sensory physiology and behaviour is presented in chapter twelve.