This Rapra Review Report examines the use of biocides in plastics with reference to material types and application requirements. The commonly available biocides are reviewed and details of their strengths and weaknesses are provided. The author reviews the frequently used test methods for fungi and bacteria, and, in an ever-changing regulatory environment, explores the influence of legislation on the current and future use of such biocides. This detailed and state-of-the-art review is supported by an indexed section containing several hundred key references and abstracts selected from the Polymer Library.