The book develops the tools to describe equilibrium thermal properties and near-equilibrium processes of finite size particles, with the emphasis on gas phase particles. Numerous examples illustrate the theory. The text offers recipes for solving commonly encountered problems arising in the description of nanophase gas particles. Each chapter contains exercises spanning from easy to advance and four appendices provide additional useful information. This revised and updated third edition provides the reader with new sections, a new chapter on kinetic energy distributions, a new appendix on probability distributions and a wealth of exercises.