This boook is my dissertation for Master of Science graduation in Civil and Environmental Engineering at University of California, Los Angeles (2009). The goal of this work is to begin a path towars the forecast of Fiber Reinforced Concrete strength in terms of loading ultimate capacitu and toughness depending on fiber geometric and mechanical properties. It would have been hard to achieve both goals in a general way in few months, but limiting the load pattern to the flexural tests on specimans and using realistic assumptions on the deformation and crack opening in a cross section it has been possible to build a simple procedure able to evaluate a realistic evolution of load vs. displacement diagrams, and toughness of the compositie material. The fiber pull-out behavior is based on several authors works, but a particular quotation is for Professor V.C. Li. I hope this work will be usefull to any researcher or designer eager to continue the research on Fiber Reinforced Concrete behavior.