The working paper is divided into two main parts. The first part is a descriptive analysis of the illicit use of biological agents by criminals and terrorists. It draws on a series of case studies documented in the second part. The case studies describe every instance identifiable in open source materials in which a perpetrator used, acquired, or threatened to use a biological agent. While the inventory of cases is clearly incomplete, it provides an empirical basis for addressing a number of important questions relating to both biocrimes and bioterrorism. This material should enable policymakers concerned with bioterrorism to make more informed decisions.