Abstract: A tool for attaching an identification tag body and a tag retainer to an ear of an animal. The tool includes a main handle member and a first bracket pivotally mounted on the main handle member. An opening in the first bracket receives a hollow boss of the tag body. A second bracket is pivotally mounted on the main handle member. A boss on the second bracket is received inside the hollow boss of the tag body when in a tag body supporting position. A link assembly is pivotally mounted on the main handle member. A drive pin member receives the tag retainer. The drive pin is resiliently mounted on the link assembly and is urged toward a position in which the tag retainer enters the hollow of the boss of the tag body as the link assembly is advanced in a retainer actuating direction. The link assembly is driven in retainer actuating direction to drive the tag retainer through the ear of the animal and into position for holding by the boss of the tag body.