A police dog is a dog that is trained specifically to assist police and similar law-enforcement personnel with their work. They can also be known as a K9 unit (a homophone for canine), this is especially prevalent in the United States.

The term is sometimes associated with German Shepherd dogs because of the long history of the use of the German Shepherd by the police and military for public order enforcement (and some forces use German Shepherds exclusively).

There are several different reasons that a police force may choose to operate a dog. These include:

• Public order enforcement dog - The 'traditional' image of a police dog is one used to enforce public order by chasing and holding suspects, or detaining suspects by virtue of the threat of it being released.
• Tracking dog - A tracking is used to locate suspects or finding missing persons or objects. Bloodhounds are often used for this task.^{[citation needed]}
• Illicit substances dog - Some dogs are used to detect illicit substances such as drugs or explosives which may be carried on a person in their effects. In many countries, Beagles are used in airports to sniff the baggage for items that are not permitted; due to their friendly nature and appearance, the beagle does not worry the passengers.^{[citation needed]}
• Cadaver dogs - Some dogs, called cadaver dogs, are trained in detecting the odor of decomposing bodies. Dogs' noses are so sensitive that they are even capable of detecting bodies that are under running water.^{[citation needed]}

Most often, police dog refers to a dog who has been trained to guard their handler, and to find, chase, or stop a fleeing suspect. Most are trained to enjoy their work, with chasing and grabbing introduced to them as tricks or games that can be played only when the handler (a police officer) gives the appropriate command. The dog's goal is not to bite to cause injury; it is to grab and hold on to the suspect at all costs, which can cause severe injury to the suspect in the process. This means that the dog grabs hard, and a fleeing suspect can be bitten and severely injured when attempting to avoid or fight off a dog. Most handlers, if possible, give the suspect a verbal warning that the dog will be set loose if they do not immediately surrender, and this is often sufficient deterrent that the dog is not needed.

Some police dog units prefer to start with a pursue and bark tactic, where the dog barks to alert the handler to his whereabouts and to intimidate the suspect and keep him from running until the police arrive. In this case, the dog usually grabs and holds only when the suspect does not halt. Others feel that the bark first, bite later strategy is not effective and prefer to always use the chase and hold strategy.^[1]

In the United States, the majority of police dogs trained for pursuit and attack are trained using commands in languages other than English. This has several advantages, in that the dog is less likely to inadvertently hear a command word in everyday conversation. Further, unless the pursued individual speaks the language in which the dog is trained, it prevents the individual from issuing a stop command or understanding the commands the handler is giving to the dog.

Most of these dogs live in their handlers' homes and interact with their family and friends on a regular basis to ensure that they remain social and pleasant animals.

A police dog and handler train and work as a team, because they must trust each other and understand each other completely when working in stressful, even dangerous, and often rapidly changing situations. Police dog teams have been accused of using excessive force in some cases, so it is critical that the human be able to manage a difficult situation wisely, to use the trained dog only as appropriate, and to be able to control the dog completely so that the dog can be called off instantly when the situation warrants.

In recognition of the valuable role these animals play in police duties and the dangers they face, there have been a number of measures to ensure their protection. These include outfitting dogs with body armor to protect them from guns and some areas have passed laws that make attacking a police dog a felony (in New Jersey, after a police dog was killed in the line of duty, the NJ General Assembly attempted to pass legislation that would treat the murder of an on-duty police dog as the same as the murder of an on-duty police officer, allowing the state attorney general or county district attorneys to pursue the death penalty). By the same token, a police dog killed in the line of duty is often given a full police funeral just like a human officer.

As of February 2007, the U.S. Transportation Security Administration currently uses 420 trained dogs to patrol 75 airports and 13 major transit systems. On September 11, 2001, the TSA only had 174 dogs in service in 39 airports.^[2]

General purpose police dogs in British police forces are usually German Shepherds, also known as Alsatians. 'Passive' drug dogs (used to sniff people as they pass to determine whether they are carrying drugs, but not to actually touch them) are often Labradors, known for their placid and friendly nature. 'Active' drug dogs (which search for drugs in locations instead of on people) and explosives dogs are usually Springer Spaniels, known for their inquisitiveness, intelligence and enthusiasm. General purpose dogs and passive drugs dogs are usually trained to search for objects as well.

Handlers and their dogs must be licensed by the Home Office, following a thirteen-week course. They are licensed as a team and handlers cannot work each others' dogs unless they undergo a licensing course with the other dog as well (which only lasts six weeks if both handler and dog are already fully-trained).

The Belgian Canine Support Group is part of the country's federal police. It has 35 dog teams. Some dogs are trained to detect drugs, human remains, hormones or fire accelerants. About a third are tracker dogs trained to find or identify living people. These teams are often deployed to earthquake areas to locate people trapped in collapsed buildings. The federal police’s explosive detector dogs are attached to the Federal Police Special Units.

The Dutch Mounted Police and Police Dog Service (DLHP) is part of the Korps landelijke politiediensten (KLPD; National Police Services Agency) and supports other units with horse patrols and specially trained dogs. The DLHP’s dogs are trained to recognize a single specific scent. They specialize in identifying scents (identifying the scent shared by an object and a person), narcotics, explosives and firearms, detecting human remains, locating drowning people and fire accelerants.

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• Alabama statute
• Alaska statute
• Arizona statute
• Arkansas statute
• California statute (Sec. 600)
• Oklahoma statute #1
• Oklahoma statute #2

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• The Police Dog Home Page
• The North American Police Work Dog Association
• Nashville Police Special Operations, K-9]

• Metropolitan Nashville Police Department

• Media related to Police dogs at Wikimedia Commons