In recent years there has been remarkable progress in our understanding of the properties of solid surfaces. Several factors which have contributed to recent developments in surface science are attributed to the advances of ultrahigh vacuum technology, modern experimental techniques, and handling of metals in very high purity. The investigations of gas-solid interac-tions, gained by various modern techniques, are reviewed on such topics as the adsorption states and binding energies of gases, surface reaction, and structure of adsorbed sarface layer on atomically clean metal surfaces.