ISO/IEC 18000-2:2009 defines the air interface for radio frequency identification (RFID) devices operating below 135 kHz. The purpose of ISO/IEC 18000-2:2009 is to provide a common technical specification for RFID devices that can be used by ISO committees developing RFID application standards. ISO/IEC 18000-2:2009 is intended to allow for compatibility and to encourage inter-operability of products in the international marketplace. ISO/IEC 18000-2:2009 defines the physical layer used for communication between the interrogator and the tag and further defines the communications protocol used in the air interface.

Two types of tag are defined by ISO/IEC 18000-2:2009: Type A and Type B, which differ only by their physical layer. Both support the same inventory (anti-collision) and protocol.

Type A tags are permanently powered by the interrogator, including during the tag-to-interrogator transmission, and operate at 125 kHz.

Type B tags are powered by the interrogator, except during the tag-to-interrogator transmission, and operate at 125 kHz or 134,2 kHz.