This book provides a unique blend of data on insect life spans, physiology, enzymology and other molecular features associated with digestion and nutrient absorption to enrich the knowledge on insects and to disclose putative molecular targets for the development of new insect control technologies and for improving insect raising procedures to be used as food and feed. With this aim, the book overviews the types of diets consumed by insects, describing their chemical components demanding digestion and discusses the evolutionary selective pressures on insects associated with feeding. Digestive enzymes are classified and detailed according to their activity on substrates and their evolutionary protein families. The technical details on how to obtain reliable enzymological parameters are discussed. The book reviews the structural changes in enzymes associated with the adaptation of insects to new diets and in avoiding natural plant inhibitors. Midgut features that enhance digestive and nutrient absorption efficiency and their underlying molecular mechanisms are described regarding insects pertaining to key points in evolution. Evolutionary trends of the mechanisms of digestion and nutrient absorption are discussed.