The industry can be divided into two primary segments: government agencies and commercial agencies. By far, the greatest number of people in emergency and protective services are working at the local level of the government. Almost every community has its own police department. In the smallest communities, a police department may have as few as one or two employees. In larger cities, the members of a police department are divided into many divisions, each with its own area of the city to patrol. A police force may have specialized divisions, such as a narcotics squad to combat illegal drugs; a vice squad to fight rape, prostitution, and related crimes; a SWAT team that can be called upon in emergency situations; a hostage rescue team; and a bomb squad. Most police departments employ a military-style ranking system. Patrol officers may become detectives. Police officers may rise through the ranks to become sergeants, lieutenants, or even the chief of police for a community. Many other people provide support for a police department, from traffic clerks and police clerks to forensic experts and polygraph examiners.

Other important areas of local law enforcement are probation and parole services. Probation officers are generally attached to the court system, while parole officers work with the correctional system. Both work in cooperation with the police department.

Sheriff departments generally operate at the county level and provide additional law enforcement efforts among the many communities in a single county. Almost every state operates its own state police department. They are often called highway patrols because one of their major responsibilities is to ensure the safety of the highways linking communities.

The U.S. Marshals Service, part of the U.S. Department of Justice, is concerned with crimes that cross state lines. Interstate crimes, as they are called, may involve the transport of stolen vehicles and goods from one state to another. U.S. marshals are responsible for tracking down wanted criminals and transporting prisoners. They also operate the federal Witness Security Program and provide security for federal courts and judges.

Enforcement of federal laws is largely the responsibility of the Federal Bureau of Investigation. The FBI oversees more than 200 separate violations, including such federal crimes as kidnapping. While still investigating all types of federal crime, the bureau's most important mandate today is to protect the American people from future terrorist attacks. The Central Intelligence Agency is primarily concerned with matters of international security, monitoring world events as they relate to the safety and interests of the United States.

There are many other public safety agencies operating at the federal level, including the Drug Enforcement Administration, the Secret Service, U.S. Customs and Border Protection, U.S. Citizenship and Immigration Services, and the Internal Revenue Service. Each agency oversees a particular jurisdiction, or responsibility, of the law. However, every federal agency provides support and cooperation to the others and they often work with state and local law enforcement agencies when investigating crimes and apprehending criminals. Since 2002, several federal agencies, including the Customs Service, the U.S. Citizenship and Immigration Services (formerly the Immigration and Naturalization Service), the Secret Service, and the Coast Guard, are now part of the Department of Homeland Security. In 2004, a special commission investigated the terrorist attacks of 2001 and made recommendations for a major overhaul of intelligence and security in the federal government. Some, but not all, of these recommendations have since been implemented.

The incarceration and rehabilitation of suspected and convicted criminals occurs at each of the local, state, and federal levels. By the 21st century, jails were being managed by a combination of local and state government agencies and for-profit private companies. This occurred as a response to the increasing numbers of people being incarcerated, but public opinion of for-profit prison management is skeptical, with people concerned that the need to generate profit creates and incentive for incarceration. Currently, the prison system operates minimum, medium, and maximum security prisons, depending on the nature of the crime and the criminal. Special prisons house mentally ill prisoners or juvenile offenders. People convicted of federal crimes are generally sent to prisons operated by the federal government. The FBI also investigates cybercrimes, those committed via the World Wide Web that frequently involve scams, hacking, and identity theft.

Private, for-profit companies such as security agencies and detective agencies work to ensure public safety as well. Many provide such services as bodyguards, security systems, armed security guards, and private investigation services in order to prevent crimes against people and property. Many private companies also work within the correctional system, operating prisons or providing corrections officers or other services. Some private companies also provide police services for universities, airports, communities, and large government facilities and installations and they may also serve as consultants or forensic investigators of computer and cybercrimes.