This book describes the ecological basis for the phenomenon of biological control, its historical development by man, the nature of entomophagy with particular reference to insects that feed on other insects, procedures for carrying out programs of biological control, and evaluation of any results attained. Although we have limited our coverage mainly to “classical biological control,” as defined above, we mention briefly other biological methods of pest control, including host plant resistance; the book then ends with a statement about the future of biological control.