Over the past three decades there has been a dramatic increase in theoretical and practical studies on insect natural enemies. This considerably updated and expanded version of a previous best-seller is an account of major aspects of the biology of predators and parasitoids, punctuated with information and advice on which experiments or observations to conduct, and how to carry them out. This book is unique among the many works on the subject, as a general text emphasizing practicalities and providing guidance on further literature.