At present, the processing of high volume of information and world wide communication are based on semiconductor technology, whereas information storage devices rely on multilayers of magnetic metals and insulators. 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 applies the Monte Carlo method to investigate the significant case of electrons in bulk GaAs. The prediction of an increase of the spin lifetime in the presence of carrier-carrier 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 extrafluctuating electric field. The experimental validation of these achievements offers valuable challenges to experimentalists.