This book examines the design of chipless RFID systems. The authors begin with the historical development of wireless identification systems and finally arrive at a representation of the chipless RFID system as a block diagram illustration. Chapter 2 is devoted to the theoretical bases for the design of chipless RFID tags and detection techniques in the reader. A rigorous mathematical formulation is presented based on the singularity expansion method (SEM) and characteristic mode theory (CMT) in order to study the scattered fields from an object in a general form. Th e authors attempt to explain some physical concepts behind the mathematical descriptions of the theories in this chapter. In Chapter 3, two design procedures based on complex natural resonance and CMT are presented for the design of the chipless RFID tag. By studying the effects of structural parameters on radiation and resonant behaviors of the tag, some design conclusions are presented in this chapter. Chapter 4 is dedicated to the time-frequency analysis of the scattered fields from chipless RFID tags. After some explanation of the time-frequency analysis techniques and issues relating to resolution in time and frequency, an efficient technique called short-time matrix pencil method (STMPM) is introduced and efficiently employed to study various scattering mechanisms. Th e performance of the proposed technique against noise is studied in this chapter. Finally in Chapter 5, an anti-collision algorithm is presented through which the positions and IDs of multiple multi-bit tags are extracted from the backscattered signal of the tags present in the reader area.