Metastable-atom de-excitation spectroscopy (MDS) is a powerful technique to study the electronic structures of the outermost atomic layers of solid surfaces. In this paper we give an outline of the mechanism of metastable-atom de-excitation followed by electron emission from surfaces. Some recent results of its application to the study on adsorption and thin film growth are reviewed and a unique role of the MDS method in charaterizing interface structures is discussed.
