Project Summary: Without comprehensive, up-to-date, and validated risk assessments, there would be no basis or focus for planning and preparedness measures designed to prevent, protect against, respond to, and recover from terrorist attacks or other hazards. It is, therefore, important to understand how these concepts are defined, measured, and addressed before conducting risk assessments. There are important distinctions among the concepts of threat, risk, and vulnerability in the context of homeland security. Risk refers to the probability or general likelihood that an attack or disaster will occur in a given area, and it is a function of three variables: threat, vulnerability, and consequence. Threat refers to the presence of a specific hazard or the likelihood that a certain type of attack or disaster will occur in the area being assessed. Vulnerability highlights the weaknesses or gaps in preparedness or the likelihood that an attack would succeed. Consequence refers to the impact of an attack or