In the United States, a special agent is an official title used to refer to certain investigators or detectives of federal, military, tribal, or state agencies who primarily serve in criminal investigatory positions. Additionally, some special agents operate in criminal intelligence, counterterrorism, or counterintelligence-based roles as well, with one or all of these roles occasionally taking precedence over criminal investigatory tasks.

Within the American federal law enforcement system, dozens of federal agencies employ federal law enforcement officers (LEOs), each with different criteria pertaining to the use of the titles special agent and agent. Most criminal investigators employed by the U.S. Department of Defense and its component departments typically utilize the title of "special agent."

Most people holding the title of "special agent" are LEOs under state and/or federal law (with some also being dual intelligence operatives such as with the FBI). These LEOs are distinctly empowered to conduct both major and minor criminal investigations and hold arrest authority. While not all federal LEOs are "special agents," nearly all special agents – with very few exceptions – are duly-sworn LEOs. This holds true at the state-level, as well, with nearly all special agents of state agencies being sworn LEOs.

In intelligence usage, "agent" may also refer to a human source or human "asset" who is recruited, trained, controlled, and employed to obtain and report information. However, within law enforcement agencies, these types of sources are often referred to as informants, confidential informants (CI—not to be confused with counterintelligence), or confidential human sources (CHS).

Federal government

Within the U.S. government, the title of Special Agent primarily designates the Criminal Investigator GS-1811 series position. However, the title is also concurrently used for General Investigator GS-1810 job series and the intelligence specialist in the GS-0132 job series according to the Office of Personnel Management (OPM) handbook. The vast majority of special agents are GS-1811 (or equivalent) Criminal Investigators. Special agents typically have at a minimum an undergraduate degree.

GS-1811: Criminal Investigator (Primary Special Agent occupation within the federal government)

GS-1810: General Investigator

GS-0132: Intelligence

FS-2501: Foreign Service Criminal Investigator (Department of State's Diplomatic Security Service)

Federal agencies

Most federal agencies, including the following, employ some type of special agent, investigator or background investigator:

Central Intelligence Agency (CIA)

CIA Office of Inspector General

Department of Agriculture (USDA)

United States Forest Service

Law Enforcement and Investigations

Office of Inspector General (USDA OIG)

Department of Commerce (USDOC)

National Oceanic and Atmospheric Administration (NOAA)

Office of Export Enforcement (OEE)

Office of Inspector General (DOC OIG)

Office of Security (OSY)

Department of Defense (DOD)

Department of the Air Force Office of Special Investigations (DAFOSI)

Defense Finance and Accounting Service (DFAS)

Defense Counterintelligence and Security Agency (DCSA)

Defense Intelligence Agency (DIA)

Defense Logistics Agency (DLA)

DLA Police

Office of the Inspector General

National Security Agency (NSA)

NSA Office of Inspector General

Naval Criminal Investigative Service (NCIS)

Department of Defense Office of Inspector General (DoD OIG)

Defense Criminal Investigative Service (DCIS)

Pentagon Force Protection Agency (PFPA)

United States Army Counterintelligence (Army CI)

United States Army Criminal Investigation Division (CID)

United States Marine Corps Criminal Investigation Division (USMC CID)

Department of Education (ED)

Office of Inspector General (ED OIG)

Department of Health and Human Services (HHS)

Food and Drug Administration (FDA)

Office of Criminal Investigations (OCI)

Office of Inspector General (HHS OIG)

Department of Homeland Security (DHS)

Coast Guard Investigative Service (CGIS)

Citizenship and Immigration Services (USCIS)

Customs and Border Protection (CBP)

Federal Protective Service (FPS)

Immigration and Customs Enforcement (ICE)

Homeland Security Investigations (HSI)

Office of Inspector General (DHS-OIG)

Transportation Security Administration (TSA)

United States Secret Service (USSS)

Department of the Interior (DOI)

Bureau of Indian Affairs Police (BIA)

Bureau of Land Management (BLM)

National Park Service (NPS)