This book provides an updated description of the most relevant types of highly nonlinear fibers. It also describes some of their actual applications for nonlinear optical signal processing. Multiple types of highly nonlinear fibers are considered, such as silica-based conventional highly nonlinear fibers, tapered fibers, photonic crystal fibers, and fibers made of highly nonlinear materials, namely lead-silicate, tellurite, bismuth oxide, and chalcogenide glasses. Several nonlinear phenomena occurring on such highly nonlinear fibers are described and used to realize different functions in the area of all-optical signal processing. Describes several nonlinear phenomena occurring on optical fibers, namely nonlinear phase modulation, parametric and stimulated scattering processes, optical solitons, and supercontinuum generation. Discusses different types of highly nonlinear fibers, namely silica-based conventional highly nonlinear fibers, tapered fibers, and photonic crystal fibers. Examines fibers made of highly nonlinear materials, namely lead-silicate, tellurite, bismuth oxide, and chalcogenide glasses. Describes the application of several nonlinear phenomena occurring on highly nonlinear fibers to realize different functions in the area of all-optical signal processing, namely optical amplification, multiwavelength sources, pulse generation, optical regeneration, wavelength conversion, and optical switching. Mario F. S. Ferreira received his PhD degree in 1992 in physics from the University of Aveiro, Portugal, where he is now a professor in the Physics Department. Between 1990 and 1991, he was at the University of Essex, UK, performing experimental work on external cavity semiconductor lasers and nonlinear optical fiber amplifiers. His research interests have been concerned with the modeling and characterization of multisection semiconductor lasers, quantum well lasers, optical fiber amplifiers and lasers, soliton propagation, nanophotonics, optical sensors, polarization, and nonlinear effects in optical fibers. He has written more than 400 scientific journal and conference publications and several books in the area of mathematical physics, optics, and photonics. He has served as chair and committee member of multiple international conferences, as well as guest editor and advisory board member of several international journals.