Refractive-index nonlinearities have negligible e ect on the performance of short-haul ÿber-optic communication links utilizing electronic repeaters. However, in long links, nonlinearities can cause severe signal degradations. To mitigate nonlinear e ects, a new generation of ÿbers, referred to as large e ective-area ÿbers, have been introduced in recent years. This paper reviews the latest research and development work on these ÿbers conducted by several research groups around the world. Attention is focused on a class of large e ective-area ÿbers that are based on a depressed-core multiple-cladding design. Another important issue in long-haul and high capacity ÿber optic systems is the polarization-mode dispersion (PMD) which has been recognized as a serious limiting factor. In this paper, an improved ÿber design is proposed which, in addition to providing large e ective-area and low bending loss, eliminates PMD due to elliptical deformation in the single-mode wavelength region. Furthermore, this design is allowed to provide a small chromatic dispersion about few ps=nm km, in order to overcome four-wave mixing e ects.