The ISO 15693 Standard
ISO15693 is a series of international, vendor-independent standards for vicinity RFID. It operates on 13.56MHz and uses magnetic coupling between the reader (VCD) and transponder (VICC). You can purchase the standard documents from ISO. The final committee drafts can be downloaded for free at waazaa.org. These documents are Final Comittee Drafts:
ISO 15693-1: This part describes the physical characteristics.
ISO 15693-2: This part describes the radio frequency power and signal interface.
ISO 15693-3: This part describes the anti-collision and transmission protocol.