This book highlights the recent scientific and technological innovations of various optical and optoelectronic fibers based on different functional structures and materials. Advanced optical and optoelectronic fibers locate at the intersection of many disciplines ranging from optical waveguides, optoelectronics, material engineering, micro/nanofabrication, and neural interfaces to wearable devices. The book covers the major developments on fiber materials, such as semiconductors, metals, polymers, and soft glasses, as well as novel in-fiber structures. Different functionalities are also summarized, including sensing, light guidance, lasing, and material engineering toward full system integration. The book is a valuable resource for researchers, engineers, and graduate students engaged in the study of optical and optoelectronic fibers.