Molecular clusters have many key uses ranging from novel fuel and material research to computational biology applications, however, they are not easily predictable. Modeling their behavior requires unique computational techniques. Rather than cover every marginally feasible method, this book discusses only those shown to be the most successful, such as the path integral methods in statistical mechanics and the diffusion Monte Carlo approach. Written to be accessible to an audience as broad as the uses of clusters, the author employs a guided inquiry style and, unlike similar works, ventures from classical simulations of liquids, to cover quantum mechanic simulations for atomic and molecular aggregates.