The U.S. Food and Drug Administration (FDA) uses regulatory action criteria for filth and extraneous materials to evaluate adulteration of food products. The criteria are organized into three categories: health hazards, indicators of insanitation, and natural or unavoidable defects. The health hazard category includes criteria for physical, chemical, and microbiological hazards associated with filth and extraneous materials. The health hazard category encompasses criteria for HACCP (Hazard Analysis and Critical Control Point) hazards and HACCP contributing factors. The indicators of insanitation category includes criteria for visibly objectionable contaminants, contamination from commensal pests, and other types of contamination that are associated with insanitary conditions in food processing and storage facilities. The natural or unavoidable category includes criteria for harmless, naturally occurring defects and contaminants. A decision tree is presented for the sequential application of regulatory action criteria for filth and extraneous materials associated with each category and with each type of filth or extraneous material in the three categories. This final report of a series in the development of a transparent science base for a revised FDA regulatory policy in the area of filth and extraneous materials in food includes a comprehensive list of the references that form the science base for the FDA regulatory policy.