The aim of my research activity is the study of metallic nanoparticles and nanoalloys (i.e. bi- or multi-metallic nanoparticles) by computational methods, with special attention to the out-of-equilibrium phenomena involving such systems. Nanoparticles growth process from a starting metallic vapour and their evolution from out-of-equilibrium configurations towards the most stable ones are two interesting examples of such phenomena, which are widely studied from both the theoretical and experimental point of view. The numerical method I use is Molecular Dynamics, a well-known and simple technique which is able to reproduce the evolution of a given system in a realistic way. Thanks to the collaborations between my research group and some experimental groups (in France, UK, Japan) I have often the opportunity to compare the simulations results with experimental data, and thus to achieve a better knowledge of the systems and phenomena I study.