An animal ear tag having interfitting male (5) and female (6, 21) parts for fixing the tag has a chamber (14) inside the male part (5) for receiving a cylindrical electronic responder (15, 15a), which may have a diameter of up to 3 mm and a length of up to 20 mm. The male part (5) is preferably wholly or partly formed of plastics material. An identification index encoded in the responder is also represented visually on the tag. The male and female parts are preferably mounted at opposite ends of a looped strip (1).
