The paper reviews both the properties and the applications of core-excited metastable atoms. The production of these atoms by microwaves, pulsed hollow-cathode discharges, and laser-produced x rays is described. We discuss the application of these atoms to several new types of spectroscopy that allow autoionizing linewidths as narrow as 0.1 cm' to be measured. The application of these metastables to the generation of picosecond-timescale soft-xray pulses and to XUV lasers is also discussed.