Since the 1970s, optical fibers have undergone considerable development and are now used in a very wide range of applications, covering telecommunications, the environment, medical applications, etc., thanks to the development of amplifiers, lasers, and sensors. Such progress has been made possible by the considerable work carried out to improve the transparency of optical fibers, i.e., by removing absorbing centers (such as iron ions) and structural and compositional heterogeneity. In contrast to this approach, a new family of optical fibers has been developed in recent years, incorporating heterogeneity, such as dielectric nanoparticles. Such fibers were first envisaged as a means of locally modifying the chemical and structural environment of luminescent ions (rare-earth and transition metal ions) in order to offer new fiber lasers and amplifiers. However, light scattering induced by the nanoparticles imposes severe drawbacks for those applications. Very recently, light scattering has been reported to be of great interest to developing sensors (temperature, stress, chemistry, biology, etc.). To exploit the light-scattering property, two main methods wereused to analyzed the sensors, based on optical backscatter reflectometry and transmission reflexion analysis. This presentation will review these fibers, presenting the fabrication processes, the fundamental issues involved in nanoparticle formation, and their different applications.