The new field of semiconductor spintronics represents a possible direction towards the development of hybrid devices that could perform logic operations, communication and storage, within the same material technology. This book provides a critical analysis of the mechanisms responsible of spin relaxation and applied the Monte Carlo method to investigate the significant case of electrons in bulk GaAs. It includes the results obtained by Dr. Stefano Spezia during his three-year Ph.D. in Applied Physics, under the supervision of Prof. Dominique Persano Adorno, and in collaboration with Dr. Nicola Pizzolato and Prof. Bernardo Spagnolo, at the Department of Physics of the University of Palermo (Italy). The prediction of an increase of the spin lifetime in the presence of e-e scattering as well as at increasing lattice temperatures are relevant results from both a fundamental and an applied point of view. Also remarkable is the possibility to increase the spin lifetime by the simultaneous application of high fields and an external noise controlled by an extra fluctuating electric field. The experimental validation of these achievements offers valuable challenges to experimentalists.