A police dog, often referred to as a "K-9" (which is a homophone of canine) in some areas, is a dog that is trained specifically to assist police and other law-enforcement personnel in their work. The most commonly used breed is the German Shepherd, although now Belgian Malinois are also fairly popular dogs to use. In many jurisdictions the intentional injuring or killing of a police dog is a felony, subjecting the perpetrator to harsher penalties than those in the statutes embodied in local animal cruelty laws, just as an assault on a human police officer is often a more serious offense than the same assault on a non-officer. A growing number of law-enforcement organizations outfit dogs with ballistic vests, and some make the dogs sworn officers, with their own police badges and IDs. Furthermore, a police dog killed in the line of duty is often given a full police funeral.

Some breeds are used to enforce public order by chasing and holding suspects, or detaining suspects by the threat of being released, either by direct apprehension or a method known as Bark and Hold. German Shepherd Dogs and Belgian Malinois are most commonly used because of their availability (see List of police dog breeds); however other dog breeds have also contributed, such as Dutch Shepherds, Rottweilers, Boxers, Doberman Pinschers, Giant Schnauzers, American Pit Bull Terriers, and American Staffordshire Terriers.

A police officer (also known as a policeman or policewoman, and constable in some forces, particularly in the United Kingdom and other Commonwealth nations) is a warranted employee of a police force. In the United States, "officer" is the formal name of the lowest police rank; in many other countries "officer" is a generic term not specifying a particular rank, and the lowest rank is often "constable". Police officers are generally charged with the apprehension of criminals and the prevention and detection of crime, and the maintenance of public order. Police officers may be sworn to an oath, and have the power to arrest people and detain them for a limited time, along with other duties and powers.

Some police officers may also be trained in special duties, such as counter-terrorism, surveillance, child protection, VIP protection, and investigation techniques into major crime, including fraud, rape, murder and drug trafficking.

Responsibilities of a police officer are varied, and may differ greatly from within one political context to another. Typical duties relate to keeping the peace, law enforcement, protection of people and property, and the investigation of crimes. Officers are expected to respond to a variety of situations that may arise while they are on duty. Rules and guidelines dictate how an officer should behave within the community, and in many contexts restrictions are placed on what the uniformed officer wears. In some countries, rules and procedures dictate that a police officer is obliged to intervene in a criminal incident, even if they are off-duty. Police officers in nearly all countries retain their lawful powers, while off duty.

The Dogs were a 1990s hip hop group consisting of Disco Rick, Keith Bell, Labrant Dennis and Fergus "Cracked Up" Smith, best known for "Crack Rock," their hit single with the chant "Yo' Mama's on Crack Rock!" The group released three studio albums The Dogs in 1990, Beware of The Dogs in 1991 and K-9 Bass in 1992.

Labrant Dennis was arrested in May 1996 for the double murder of Marlin Barnes, a University of Miami football player, and Timwaneka Lumpkin, his exgirlfriend.