Insects, pests and weeds are responsible for substantial loss of crops and reduced food supplies, poorer quality of agricultural products, economic hardship for growers and processor. Generally, chemical control methods are neither always economical nor are they effective and may have associated unwanted health, safety and environmental risks. Biological control involves use of beneficial biological agents to control pests and offers an environmental friendly approach to the effective management of plant diseases and weeds. The chapters are written by well recognized group leaders in the field. This book provides a comprehensive account of interaction of host and pests, and development of biological control agents for practical applications in crops management utilizing inherent defence mechanism, induced stimulation and biological control agents. The contents are divided into the following sections: General biology of plant defence, Use of natural compounds for biological control, Use of biological agents, Mechanism of action and Commercial aspects. The book will be useful for academicians, researcher and industries involved in study and manufacturing these products.