Abstract: This work describes the concept, design, fabrication, and characterization of delay-based radio frequency identification (RFID) tags and RFID-based sensor tags, representing a novel RFID technology. The presented delay-based RFID concept is based on the LC-delay-line and transmission-delay-line based approaches. The proposed concept allows the realization of RFIDs and RFID-based sensor tags at any allowed radio frequency, with the limitation of realizing delay elements capable of producing required delays. The RFID configurations presented in this work are for operation at 915 MHz. Simulations are used to design and optimize components and devices that constitute the tags, and to integrate them to realize tags of different configuration. A set of fabrication processes has been developed for the realization of the tag. Characterization and field testing of these tags show that delay-based RFID approach can be used to make passive tags at ultra high frequency (UHF) and other allowed frequencies. Delay-based tags have the advantages of time domain operation, and the feasibility of complying with FCC regulations. However, size, need of isolators and circulator, and design constraints in producing higher number of bits are some of the concerns that need to be further addressed. In summary, this dissertation work presents a viable alternative RFID approach based on the delay line concept. The results obtained show great promise for further development and optimization of this approach for a wide range of commercial applications.