This book bridges the gap between theory and experiment through the Monte Carlo method. Photon transport studies in nuclear sciences is incomplete without the application of statistical techniques. Here PENELOPE, which is one of the most advanced Monte Carlo codes, has been applied, on the platform of FORTRAN G77, using photon energies of Co, Cs and Am sources, to reveal complex phenomena which cannot be accomplished analytically or through laboratory experiments. The author highlighted the essentials of Monte Carlo methods and went further by developing a random number generator which can replace the existing one in PENELOPE. Lead and aluminum material slabs which are widely used as nuclear shields and detector end-cup housing have been used and photon paths, through them, are simulated and presented as pictorial showers which are good pedagogical tools in nuclear radiation studies. Gamma ray shielding depths are determined with safety, ease and precision without consulting physical experiment. Transmitted, absorbed and backscattered photons through the slabs have been simulated. Finally the author validated results which clearly illustrates the importance of the book.