Photonic Integrated Circuits for Sensing Applications delves into the fascinating world of sensors within the realm of integrated photonics. The book begins with a historical overview, tracing the evolution of spectroscopic sensing techniques such as FTIR, Raman, SPR, and reflectometry, each contributing to the field's growth. It emphasizes the transformative potential of photonic integrated circuit (PIC) sensor systems by showcasing their advantages in achieving low SWAP-C metrics (size, weight, power, and cost) while maintaining high performance. Complete with technical insights, the book sets the stage for understanding how PICs are revolutionizing sensing applications across diverse industries. Beyond the introductory scope, the book thoroughly examines the components that constitute PIC sensor systems, including waveguides (operating below and above 1550 nm), ring resonators, photonic crystals, and MZ interferometers. It also explores integrated systems designed for chem-bio sensing applications, leveraging biofunctionalization and sorbent technologies. With attention to manufacturing scalability, topics such as materials, PDK development, and sensor packaging are addressed, ensuring readers grasp the practical aspects of producing advanced sensor systems at scale.