Chapter One presents a study on application of Monte Carlo simulation in reliability assessment of composite electric power systems. Chapter Two develops a PK/PD model to evaluate, by Monte Carlo simulation as a data maximisation strategy, the antiviral activity of two stavudine formulations: conventional stavudine and stavudine-gold nanoparticles (stavudine-AuNPs). In Chapter Three, the magnetic properties of the kagomé lattice is studied with RudermanKittelKasuyaYosida (RKKY) exchange interactions in a spin-7/2 and alternate mixed spin-5/2 and spin-2 Ising model on the Bethe lattice by using the Monte Carlo simulations.