Metastable Atom De-excitation Spectroscopy (MDS) provides a powerful technique with which to investigate surface electronic structure with unparalleled surface specificity. In this technique a thermal energy beam of noble-gas metastable atoms is directed at the surface to be studied and the kinetic energy distribution of ejected electrons that result from metastable atom de-excitation is measured. Although the measured distribution contains information about the electronic structure of the outermost surface layer, its detailed analysis requires knowledge of the dynamics of the metastable atom-surface interaction. In the present work, these dynamics have been investigated directly by use of spin-labeling techniques. The electron spins on the incident metastable atoms are polarized and the spin-polarization of the ejected electrons is measured with a Mott polarimeter. Energy-integrated electron spin-polarization (ESP) measurements for Pd(110) and energy-resolved ESP measurements for Cu(100) surfaces under a variety of conditions indicate that metastable atom-surface interactions are more complex than has been assumed in past MDS studies. Spin-polarized MDS has also proven useful in the study of surface magnetism. The present work includes a study of the surface electronic and magnetic structure of the Fe(110) surface. Results indicate an interesting reversal of surface electron spin-polarization for Fe(110) surfaces exposed to oxygen.