Single-atom tips can be used as ideal point sources of electron beams. Noble-metal covered W(111) single-atom tips can be reliably prepared and their lifetimes are long enough for real applications. These tips are both thermally and chemically stable and can be regenerated in vacuum when accidentally damaged or contaminated. The atomic stacking remains the same each time it is regenerated. The small opening angle, smallest emitting area, high brightness, high spatial coherence, and high stability of these single-atom electron sources make them highly desirable for many applications. Both the brightness and spatial coherency of these electron sources are orders of magnitude better than those of the state-of-the-art electron sources used in electron microscopes. Application of these sources may significantly improve the performance and expand the capabilities of current electron microscopes and would probably open up many new possibilities in electron-beam based techniques.