Mail and postal facilities are tempting targets for theft and other criminal acts. Approximately 800,000 U.S. Postal Service (USPS) employees process about 700 million pieces of mail daily at almost 38,000 facilities nationwide. Criminals attack letter carriers to get mail containing valuables and burglarize postal facilities to get cash and money orders. These activities at USPS facilities can put at risk the integrity of the mail and the safety of employees, customers, and assets. We looked at physical security measures at large facilities that perform automated mail-sorting functions, which on the basis of discussions with USPS, we defined as "core" facilities. Specifically, our objectives were to provide information on (1) what USPS has determined to be the physical security requirements at core facilities, (2) what security measures have been implemented and what security problems exist at USPS core facilities, and (3) what are USPS's plans to respond to identified security problems.