This book presents a new radio frequency identification chipless tag operating in the frequency range of 4-7 GHz. The tag consists of triangle microstrip filters. The bits are encoded into the spectrum hence the tag has a unique spectral signature. The simple opening of the triangle sides shifts the resonant frequency of the triangle resonator to a frequency outside the designed band.Another chipless tag operating in the frequency range of 3.5-4.3 GHz is considered. It focuses on the integration of the antenna and multiresonator structures to form the chipless RFID tag. The tag consists of triangle microstrip filters with cutting slots in the triangle sides.A compact printable orientation independent chipless RFID tag is presented. The tag consists of a circular patch loaded with multiple semi-circular slot resonators. This symmetric frequency domain based tag has the advantage to be read from any orientation with the reader antennas. the tag consists of horizontally and vertically polarized shaped slot resonators. It can be used as an orientation independent linearly polarized tag at the half data capacity of the dual polarized setup. The integration of temperature sensor with tag