Abstract: A tool for applying an identification tag body and a tag retainer to an ear of an animal. The tool includes a main handle member on which a tag body is mounted, a swinging bracket pivotally mounted on the main handle member, a second handle member pivotally connected to the swinging bracket, a first sliding link member pivotally connected to the second handle member, and a second sliding link member pivotally connected to the second handle member. The tag retainer is mounted on the swinging bracket. As the swinging bracket swings, the tag retainer can pass through the animal's ear and enter a boss of the tag body for locking therein. Support structure on each of the sliding link members can engage support pins mounted on the main handle member so that linkage of the tool can advance in two stages as the handles are advanced toward each other. The support structure of the sliding link members can come free of the associated support pins, one at a time.