Free clusters in vacuum are of fundamental rather than practical interest. Structure and dynamics can be studied as a function of size in the absence of any interaction with the environment. Even the exchange of energy can be controlled. The melting temperature and the latent heat and entropy of melting are studied and the influence of incomplete geometric shells addressed, revealing fascinating phenomena such as negative heat capacities (meaning that a cluster cools when it absorbs energy). Furthermore, such systems are sufficiently simple for accurate theoretical investigations. The dynamics of atoms at the surface is compared with that in interior shells, revealing details of surface premelting. In this respect it is unexpected that the cases of icosahedral Pt13 and Ni13 are quite different. Thin layers behave in many respects similarly to clusters.