This publication specifies the National Institute of Justice (NIJ) ballistic protection levels and associated test threats identified by U.S. law enforcement as representative of current prevalent threats in the United States. This document is the first of its kind published by NIJ. Prior versions of NIJ standards for ballistic-resistant body armor, helmets, and materials all included ballistic protection levels within the respective documents. These standards were published at different times—and the threats associated with the different ballistic protection levels often differed as the threats evolved over time. This document seeks to unify ballistic protection levels across a range of ballistic-resistant products used by U.S. law enforcement. It is divided into four sections and three appendices. Separating the ballistic protection levels and test threats specified here in NIJ Standard 0123.00 from particular ballistic equipment performance requirements and test methodology allows for greater interoperability among standards that are applicable to ballistic-resistant equipment. This modularity gives NIJ the ability to be responsive to new developments regarding threats while simultaneously reducing the administrative burden to update several performance standards that would use identical protection levels and test threat information.