Printed flexible electronics have many applications in sensor networks, including wearable health monitoring. Wireless communication is an important aspect of nodes of a sensor network. Passive RFID is one approach well suited for communication with flexible sensors. A flexible passive RFID tag includes a printed antenna and an RF integrated circuit (RFIC). This report describes both printed antennas and RFIC integration. First, antennas fabricated with four different printing techniques–inkjet printing, spray coating, stencil printing, and screen printing–are compared. It is found that inkjet printed antennas have high losses because of their thinness while the other three techniques have similar performance. Next, materials and techniques for mounting rigid components such as the RFIC are discussed. Finally, complete functional tags operating in the UHF RFID band are demonstrated by sending data from on-board temperature sensors. These tags have a read range of up to 40 cm.