Military identification tag, also informally known as dog tag, is a common term for a specific type of identification tag worn by military personnel. The tags' primary use is for the identification of casualties; they have information about the individual written on them, including identification and essential basic medical information such as blood type and history of inoculations. They may indicate a religious preference as well. The term arose and became popular because of the tags' resemblance to animal registration tags.

The earliest mention of an identification tag for soldiers comes in Polyaenus (Stratagems 1.17) where the Spartans wrote their names on sticks tied to their left wrists. A type of dog tag ("signaculum") was given to the Roman legionary at the moment of enrollment. The legionary "signaculum" was a lead disk with a leather string, worn around the neck, with the name of the recruit and the indication of the legion of which the recruit was part. This procedure, together with enrollment in the list of recruits, was made at the beginning of a four-month probatory period (Latin: probatio). The recruit obtained the military status only after the oath of allegiance (Latin: signaculum) at the end of "probatio", meaning that from a legal point of view the "signaculum" was given to a subject who was no longer a civilian, but not yet in the military.

In more recent times, dog tags were provided to Chinese soldiers as early as the mid-19th century. During the Taiping revolt (1851–66), both the Imperialists (i.e., the Chinese Imperial Army regular servicemen) and those Taiping rebels wearing a uniform wore wooden dog tags at the belt, bearing the soldier's name, age, birthplace, unit, and date of enlistment.

During the American Civil War from 1861 to 1865, some soldiers pinned paper notes with their name and home address to the backs of their coats. Other soldiers stenciled identification on their knapsacks or scratched it in the soft lead backing of their army belt buckles.

Manufacturers of identification badges recognized a market and began advertising in periodicals. Their pins were usually shaped to suggest a branch of service, and engraved with the soldier's name and unit.

Machine-stamped tags were also made of brass or lead with a hole and usually had (on one side) an eagle or shield, and such phrases as "War for the Union" or "Liberty, Union, and Equality". The other side had the soldier's name and unit, and sometimes a list of battles in which he had participated.

On a volunteer basis Prussian soldiers had decided to wear identification tags in the Austro-Prussian War of 1866. However, many rejected dog tags as a bad omen for their lives. So until eight months after the Battle of Königgrätz, with almost 8,900 Prussian casualties, only 429 of them could be identified.

With the formation of the North German Confederation in 1867 Prussian, military regulations became binding for the militaries of all North German member states via the Instruction on the Medical Corps Organisation of the Army Afield (German: Instruktion über das Sanitätswesen der Armee im Felde) issued on 29 April 1869. Identification tags (German: Erkennungsmarke, lit. 'Recognition mark') were to be handed out to each soldier before deployment afield.