Radio Frequency Identification (RFID) systems have been around for over 50 years, starting with the pioneering radar transponder work of the MIT Radiation Laboratory. Today, the acronym RFID typically refers to single chip, passive transponders operating at 125KHz, 13.56MHz, or UHF (915MHz) that are widely used for access control, electronic toll collection, automotive anti-theft, and other closed system applications. Recent interest has focused on supply chain management applications for RFID, where RFID tags are used to augment the bar code to provide a case- and item-level view into complex supply chains. This revolution is being aggressively driven by retailers such as Wal-Mart, consumer packaged goods manufacturers like Gillette, and the Department of Defense, all of which have complex supply chain systems that could be made more efficient by using RFID. This talk will provide a brief historical overview of the field, show some examples of the current state of the art in RFID, and then explain the basic physical principles of operation of a UHF RFID tag, using a working RFID system to show these concepts. Questions about RFID privacy will also be addressed.