This book is intended to provide a guidance through the properties of photonic crystal fibers, with a specific focus on the telecommunication aspects. The authors believe that photonic crystal fibers can revolutionize the field of guided optics and its applications, especially when considering signal processing and specific functions rather than the usage in long distance transmission. They provide a deep analysis of how the physical and geometrical characteristics of these new fibers can be tailored to achieve the goal of ad hoc performances, using the powerful numerical approach of the finite element method, and keeping in mind the possibilities and limits of photonic crystal fiber fabrication technology. The book will thus benefit researchers with an interest to explore this field of telecommunication, looking at current as well as emerging applications.