The scientific basis for successful biological control has been a relentlessly pursued but elusive goal. Nevertheless there has been progress. Some of this has come from retrospective approaches which examine the average behavior of many biological control systems to look for consistent patterns. Thus, we arrive at empirical rules such as ‘Importation of parasitoids that have maximum parasitism rates of less than 30% in the home region are doomed to failure or at best partial success.’ Such rules, when true, are useful, but it is important to better characterize successful introductions in order to refine our ability to make accurate predictions. In other words, what are the specific attributes of biological control agents and the systems in which they operate that are likely to enhance success? The tools of the theoretician can be used to explore the effects of such attributes on the dynamic properties of biological control systems and the ability of agents to suppress pest populations. Biological control systems are after all simply systems of interacting populations that should follow the same rules as natural systems, at least to some extent. Although it has been argued that traditional population dynamic theory has been of little practical use in biocontrol, modern theoretical developments attending to the complexities of real populations and their contexts are more promising. The application of recent theoretical advances to the problem of biological control is the concern of this book.