The decision to write a book about the practical aspects of the baculovirus expression system stems from the numerous phone calls for help we have had, and from the many visitors to our labora­ tories requiring assistance to find the elusive polyhedrin-negative virus containing their favourite gene. We have also organized two expression system workshops and from the manuals we wrote for these, it seemed a logical progression to extend them into book form. We appreciate that those who are 'old-hands' at the baculovirus expression system may have differing views on some of our procedures, but the methods in this book are presented in the light of our own experiences in the laboratory and from our practical workshops, and we hope that the book will be especially useful to those new to the system. The first three chapters give the background information to the baculovirus expression system, and includes advice on how to choose the right transfer vector and discusses the various methods that are available to select recombinant viruses. The practical chapters concentrate on those aspects which are novel to the baculovirus system (insect cell culture, virus amplification and titration, etc. ) and, in general, leave the standard molecular biological techniques to the other excellent laboratory manuals that are available. However, for completeness sake and to avoid constant reference to other manuals, we have included brief details of some standard techniques where they are integral to the success of the baculovirus protocols.