Biological pesticides are increasingly finding therr place in IPM and increasing numbers of products are making therr way to the marketplace. Particularly in China, Latin America and Australia, implementation is proceeding on a large scale. However, in the USA and Europe, registration procedures for insect pathogens to be used for insect control have been established that requrre low levels of risk, resulting in costs of retarding the implementation of microbial agents. This book provides a review of the state of the art of studies on the envrronmental impact of microbial insecticides. It originates from a Society for Invertebrate Pathology Microbial Control Division Symposium .. Assessment of envrronmental safety of biological insecticides", organised in collaboration with the EU-ERBIC research project (FAIR5-CT97-3489). This symposium was initiated by Heikki Hokkanen and Chris Lomer, and was held at the SIP Annual Meeting in 2001 in The Netherlands. The emphasis in this book is on large scale use of microbial agents for insect control, demonstrating how this use has been proceeding with minimal envrron mental impact. This book is intended to be of use to regulatory authorities in determining whether further studies in eertain areas are necessary and how to conduct them if needed, or whether sufficient information has been collected already to permit fuH registration of many of these biological control agents.