A law enforcement officer (LEO), or peace officer in North American English, is a public-sector employee whose duties primarily involve the enforcement of laws. The phrase can include campaign disclosure specialists, local police officers, prosecutors (who are law enforcement officers but not peace officers), municipal law enforcement officers, health inspectors, SWAT officers, customs officers, lawyers, state troopers, federal agents, secret agents, special investigators, coast guards, border patrol officers, judges, district attorney, bounty hunters, gendarmerie officers, immigration officers, private investigators, court officers, probation officers, parole officers, arson investigators, auxiliary officers, animal control officers, game wardens, park rangers, county sheriff's deputies, constables, marshals, detention officers, correction officers, sworn campus police officers and public safety officers (at public and private institutions). Security guards are not law enforcement officers, unless they have been granted powers to enforce particular laws, such as those accredited under a community safety accreditation scheme such as a security police officer.

Modern legal codes use the term peace officer (or in some jurisdictions, law enforcement officer) to include every person vested by the legislating state with law enforcement authority—traditionally, anyone "sworn, badged, and armable" who can arrest, or refer such arrest for a criminal prosecution. Hence, city police officers, county sheriffs' deputies, state troopers and in some states corrections officers are usually vested with the same authority within a given jurisdiction. Contract security officers may enforce certain laws and administrative regulations, which may include detainment or apprehension authority, including arresting. Peace officers may also be able to perform all duties that a law enforcement officer is tasked with, but may or may not be armed with a weapon.