Published Article / While the adoption rate of Radio Frequency Identification (RFID) technology is increasing, mass-market adoption will not be achieved until a few major challenges are addressed. These challenges are: privacy, security and costs from the end-user's view point and limited power supply to the tag from the engineering perspective. We discuss the research efforts aimed at addressing these challenges. We focus our attention on research in: RFID privacy and security, antennas, polymer electronics-based RFID devices, power management circuits and techniques, and efficient RF spectrum utilization. We conclude by drawing attention to three additional areas that we believe are in need of more research.