A police dog is a dog that is trained specifically to assist police and similar law-enforcement personnel with their work. They are also known in the United States as police K9s (a play on words; a homophone for canine).

The term is sometimes also used in the common parlance of several countries to refer to any German Shepherd Dog because of the long history of the use of the German Shepherd by the police and military; in some nations German Shepherds are the only dogs used by those forces. Almost all dog breeds that are trained for police work originate from Germanic and Romance countries.

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 bulletproof vests to protect them from guns and some areas have passed laws that make attacking a police dog a felony.