Radio Frequency Identification Tags (RFID) are useful tiny radio transmitters that can be placed on (or in) almost anything. While very useful for tracking animals and keeping inventory in order, there is a stark danger to privacy and freedom if this technology is allowed to be implemented on humans as well.
Not only is there a great interest in using them this way, the technology is being actively developed. If you want to know all there is to know about what companies plan to do with RFID, Spychips by Katherine Albrecht and Liz McIntyre is an excellent resource.
Each hypothetical situation is backed by company brochures, filed patents, and trade show information that shows exactly what companies plan to (and are) doing with RFID. Make sure to get this book and become more informed about why you should cringe the next time they want to put RFID on or in you.