This chapter explores the sensing capabilities of chipless RFID tags, highlighting their potential applications across various sensing domains. It begins with an overview of the transduction principles underlying chipless tags, followed by a discussion on the design of frequency-coded (FC) tags specifically tailored for sensing applications. The chapter also covers various methods for analyzing and interpreting the signals generated by chipless tags in different sensing scenarios. To illustrate these concepts, the chapter concludes with several examples of chipless RFID sensors in practical applications, showcasing their versatility and effectiveness in real-world.