An ear tag is a plastic or metal object used for identification of domestic livestock and other animals. If the ear tag uses Radio Frequency Identification RFID technology, then it is often referred to as an electronic ear tag. Electronic ear tags conform international standards ISO 11784 and ISO 11785 working at 134,2 kHz, as well as ISO/IEC 18000-6C operating in the UHF spectrum. There are other non-standard systems such as Destron working at 125 kHz. Although there are many shapes of ear tags, the main types in current use are as follows:

• Flag-shaped ear tag: two discs joined through the ear, one or both bearing a wide, flat plastic surface on which identification details are written or printed in large, easily legible script.
• Button-shaped ear tag: two discs joined through the ear.
• Plastic clip ear tag: a moulded plastic strip, folded over the edge of the ear and joined through it.
• Metal ear tag: an aluminium, steel or brass rectangle with sharp points, clipped over the edge of the ear, with the identification stamped into it.

Each of these except the metal type may carry a RFID chip, which normally carries an electronic version of the same identification number