At the beginning there is a brief overview of all RFID systems and many applications. The RFID standards and frequency ranges are explained in more detail. The UHF RFID system is also described in detail. Various reader concepts are discussed in detail. The RFID tag structure is also explained. The protocols and regulations follow. The development of front-end circuits is dealt with in the most detail. Similar to radio systems in full-duplex operation, self-generated crosstalk must also be suppressed in RFID technology, which requires, among other things, greater circuitry. This chapter is rounded off with a presentation of the boundary conditions of level plans, which are necessary for every RF system development.