The approach to thermodynamic equilibrium is the ultimate driving force in determining the configuration of surface structures. In adsorbate and thin film structures such macroscopic thermodynamic concepts may be used to predict the kinetics of islanding, clustering and other fundamental surface processes. In this paper we describe experimental and theoretical studies of cluster growth mechanisms which involve surface diffusion, adsorbate/adsorbate interactions, and surface energy concepts. We show that the time and temperature dependence of growth can be described in terms of a cluster ripening mechanism, the mass transport of material driven by surface concentration gradients. Since the limiting process for the mass transport is surface diffusion, we consider the influence of surface structure and surface energy on the clustering rate. Examples of structures studied include, Ga, Sn, and Ge on Si and As terminated Si surfaces.