radio-frequency identification (RFID), a technology that uses radio waves to transmit data and uniquely identify an animal, person, or thing. An RFID system typically consists of a tag and a reader. The tag, or transponder, contains information identifying an item or specifying a condition or state; the information is stored on a microchip that is attached to an antenna. The reader communicates with the tag and reads the information into its memory. The tag typically contains a unique serial number for identification, and may have other data, such as a customers' account number or a dog's registration information. Some tags can also receive new data, for example, an item's location during shipment for tracking purposes.

An RFID system is broadly similar to barcode systems, where information is transferred optically, but RFID has several advantages with respect to barcode technology: the capacity to store large amounts of data, the ability to read many tags simultaneously, and the ability to gather data without direct contact or line-of-sight scanning. RFID tags can be active, passive, or semipassive. Active tags employ batteries as a complete or partial power source. This increases the effective operating range of the tag and permits it to offer additional features, such as temperature sensing. Passive tags are the most common. Such tags remain dormant until triggered by radio energy emitted by the reader; that energy field then provides the power for the tag to operate. Semipassive tags, sometimes called battery-assisted tags, have a battery which powers the tag's microchip's circuitry but does not broadcast a signal to the reader. Some semipassive tags conserve power by laying dormant until they receive a signal from the reader.

Although RFID technology can be traced to the early 1920s, the first practical application was the IFF (Identification Friend or Foe) system pioneered by the British during World War II; transponders were placed into fighter planes and tanks, and readers could query them to determine whether to attack. The system was subsequently adapted for commercial and civil aviation as part of air traffic control systems. A theft-prevention system based on a tag that could store one bit (that could stand for on or off) was developed in the 1970s.

The 1970s saw RFIDs used for toll collection, and the next decade brought expanded use in supply chain management. Technological advances since then have reduced the cost and size of RFID tags, opening up a wider range of uses. RFID technology is already well established in such as livestock tracking and electronic payments, and RFID tags also are used to monitor such physical characteristics as temperature, pressure, and humidity to maintain freshness of agricultural products during shipping and storage. Paper-thin tags can now be embedded in sheets of paper, making them nearly invisible, and concerns have been raised that the technology could be used in covert monitoring schemes that pose a threat to privacy.

RFID is sometimes called dedicated short-range communication (DSRC). Historically the terms RFID and DSRC have been used synonymously to describe a technology based on tags and readers. More recently, however, DSRC has been used to describe the segment of the portion of the radio spectrum allocated to RFID applications.