Abstract: Condensed phases may be considered as infinite structures of polymerized molecules. In the case of weak intermolecular interactions "bulk" properties can be accurately modeled by the corresponding properties of clusters. Especially interesting is the evolution of the structures and properties from a single molecule or bare ion to the "bulk" phase. Modern experimental and theoretical studies provide data on such an evolution. The cohesion energy of molecules in a urea crystal, the position of Cl- in the water solution, and interactions of proton in argon environment provide examples of such studies. The present chapter discusses applications of the cluster model to the predictions of the above characteristics of the selected condense phase species.