Abstract: The invention comprises the combination of an animal ear tag and an applicator for inserting the tag into the ear. The tag has a neck portion at one side that terminates in a lateral extension of a T-shape. The applicator includes a flat, elongated knife blade, extendible from and retractible within a cylindrical housing therefor. Located rearwardly of an arrow shape cutting edge on the blade are finger means for releasably holding the lateral extension against a side of the knife blade with the cross arm of the extension located forwardly. On insertion of the blade through the ear, the cross arm of the lateral extension is concurrently moved through the resultant cut so that on withdrawal of the knife the cross arm of the lateral extension is along the side of the ear remote from the tag. A locking disc is then releasably secured to such cross arm to lock the tag against accidental removal from the ear.