Many different types of law enforcement agencies can be found within the various jurisdictions around the world. As a rule, each country or nation has a national, or federal, agency, as well as various state or local agencies. In addition, some jurisdictions have specialized departments whose jurisdiction is limited to certain crimes.
Most countries have one or more national law enforcement agencies. Spain, for instance, has the Policía Nacional, the People's Republic of China has the People's Armed Police, and Mexico has the Policía Federal. Within the United States, the Federal Bureau of Investigation, along with the U.S. Marshals Service, are the primary federal agencies. The US, however, has a variety of other groups that function as specialized police agencies, such as the Drug Enforcement Agency (DEA), the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF), the U.S. Immigration and Customs Enforcement (ICE), and the United States Secret Service (USSS).
Although the distribution of duties will vary from one jurisdiction to another, federal agencies are generally responsible for crimes that take place on federal property or for things that affect the nation as a whole. State or local officials are usually responsible for keeping the peace within their borders. In the United States, for example, the FBI has jurisdiction over federal crimes, such as bank robbery, high-level drug trafficking, and kidnapping. Crimes for which the FBI has jurisdiction are crimes that affect interstate commerce or have a multi-state component.
In countries that are governed as a federal republic, or collection of states, the individual states often have their own law enforcement agencies as well. Within the United States, each state has at least one state-level police agency. Those in Mexico — officially, the United Mexican States — each have their own police agency as well. Generally, these agencies have jurisdiction over crimes committed within the state and may have concurrent jurisdiction with local law enforcement too. Many state police groups focus their enforcement efforts on state public areas, such as highways or parks, and leave enforcement efforts within cities or towns to local police.
Cities, towns, counties, or municipalities often have a police force as well. They are responsible for crime committed within the city, town, county, or municipality, and they also act as a deterrent to crime, as they frequently have a very visible presence in the area. Within these departments, duties are most often divided between patrol officers and detectives.