The Thin Blue Line is a symbol used by law enforcement, originating in the United Kingdom but now prevalent in the United States and Canada to commemorate fallen law enforcement officers and to symbolize the relationship of law enforcement in the community as the protectors of fellow civilians from criminal elements. It is an analogy to the term Thin Red Line.

Each stripe on the emblem represents certain respective figures: the blue centre line represents law enforcement, the top black stripe represents the public whilst the bottom represents the criminals. The idea behind the graphic is that law enforcement (the blue line) is what stands between the violence and victimization by criminals of the would-be victims of crime.

Proponents of the symbol assert that the identifier is intended to show support for police. In the wake of controversies over police shootings, the Thin Blue Line Flag has become popular among law enforcement personnel, their families and supporters. Originally displayed and existing as a patch, in December 2014, Thin Blue Line USA developed the Thin Blue Line American Flag in the 3 x 5 foot flag form as it exists today.