This document provides a common framework to perform microbial risk assessment (MRA). It lays out a flexible set of approaches, methods, and tools for use to conduct their microbial risk assessment and provide more transparency to the process and results. This guideline addresses issues specific to microbial risk, e.g., secondary transmission, immune status, and growth and die-off of organisms, as well as addressing concepts generic to classical chemical risk assessment. When used by participating agencies, this product will promote greater consistency in the way that participating agencies conduct their assessments and provide more transparency.