This paper introduces a novel way to implement passive RF identification (RFID) at millimeter waves. Passive operation is achieved by adding an external mixing element between the tag antenna and a standard RFID chip. The mixing element converts the RFID reader signal from millimeter waves to RFID carrier frequency-the RFID chip operates as usual. Either passive or semipassive RFID circuits at any RFID carrier frequency can be used. The reader's TX and RX ports are similarly equipped with external mixers to convert the reader output to millimeter waves and received millimeter-wave signal to RFID carrier frequency. The paper analyses the concept theoretically with a Schottky diode as the mixing element. The design and experimental demonstration of the operation at 10 GHz are presented. Using an EPC-compliant UHF tag integrated circuit and reader, a range of 30 cm is demonstrated, but range extension to over a meter is feasible.