ISO/IEC 15963:2004 describes numbering systems that are available for the identification of RF tags.
A unique ID is required as part of the write operation to RFID tags. The unique ID guarantees that the information written to a tag is unambiguously written to the correct data carrier (tag). A unique ID is also required in many read situations where the contents of the tag are tied to a specific item and that item needs to be unambiguously identified.
The unique ID may also be used

• for the traceability of the integrated circuit itself for quality control in their manufacturing process;
• for the traceability of the RF tag during its manufacturing process and along its lifetime;
• for the completion of the reading in a multi-antenna configuration;
• by the anti-collision mechanism, to inventory multiple tags in the reader's field of view;
• for the traceability of the item to which the RF tag is attached.