The mission of the United States Postal Inspection Service is to protect the U.S. Postal Service, secure the nation's mail system and ensure public trust in the mail.

As one of our country’s oldest federal law enforcement agencies, founded by Benjamin Franklin, the United States Postal Inspection Service has a long, proud, and successful history of fighting criminals who attack our nation’s postal system and misuse it to defraud, endanger, or otherwise threaten the American public. As the primary law enforcement arm of the United States Postal Service, the U.S. Postal Inspection Service is a highly specialized, professional organization performing investigative and security functions essential to a stable and sound postal system.

Congress empowered the Postal Service "to investigate postal offenses and civil matters relating to the Postal Service." Through its security and enforcement functions, the Postal Inspection Service provides assurance to American businesses for the safe exchange of funds and securities through the U.S. Mail; to postal customers of the "sanctity of the seal" in transmitting correspondence and messages; and to postal employees of a safe work environment.

As fact-finding and investigative agents, Postal Inspectors are federal law enforcement officers who carry firearms, make arrests and serve federal search warrants and subpoenas. Inspectors work closely with U.S. Attorneys, other law enforcement agencies, and local prosecutors to investigate postal cases and prepare them for court. There are approximately 1,750 Postal Inspectors stationed throughout the United States who enforce more than 200 federal laws covering investigations of crimes that adversely affect or fraudulently use the U.S. Mail and postal system.

To assist in carrying out its responsibilities, the Postal Inspection Service maintains a Security Force staffed by approximately 830 uniformed Postal Police Officers who are assigned to critical postal facilities throughout the country. The officers provide perimeter security, escort high-value mail shipments, and perform other essential protective functions. The Postal Inspection Service operates four forensic crime laboratories, strategically located in cities across the country. The labs are staffed with forensic scientists and technical specialists, who assist Inspectors in analyzing evidentiary material needed for identifying and tracing criminal suspects and in providing expert testimony for cases brought to trial.