Hazard characterization, either as part of a microbiological risk assessment or as a stand-alone process, describes the human adverse health effects that may result from ingestion of pathogenic microorganisms. Ideally, it will include quantitative information in terms of a dose-response relation and the probability of adverse outcomes. This volume provides guidelines for the characterization of hazards in food and water using a structured, six-step approach, involving a description of the process of hazard characterization; process initiation; data collection and evaluation; descriptive characterization; dose-response modelling; and review of results. Co-published with WHO.