Weeds, insects, rodents, and pathogens are major problems in agricultural and urban environments, and there is a clear need to augment chemical methods of their control with biological methods. There has been limited success in doing so because of insufficient virulence of the host-specific organisms used. Naturally occurring biological agents are in evolutionary balance with their hosts, and attaining the level of control typically desired would lead to extinction of both the control agent and its host. The main scientists working with enhancing fungal, bacterial, virus and insect biological control agents on different targets present the latest progress in overcoming the barrier of insufficient virulence. This multi-disciplinary group, with backgrounds in different aspects of biotechnologies and crop protection review their own work and that of others, and describe the approaches being used, the successes and the barriers yet to overcome in an integrated manner. The chapters were all student-tested as highly advanced lectures during a ten-day NATO Advanced Study Institute to allow the other authors and attendees to bring new ideas, approaches, and new methodologies from different fields that were then incorporated into the chapters.