The technique of producing spin‐polarized beams of H − and D − ions by the Lamb‐shift method is reviewed. Maximum useable beam intensities are shown to depend on the flux of metastable H0 (2S) or D0(2S) atoms which can be obtained with a useable beam emittance. Factors limiting this flux are discussed. Two methods of spin‐state selection, the spin‐filter, and the diabatic field‐reversal process, are discussed. The former selects atoms in a single nuclear hyperfine state and is the best method for D↘− ions; the latter yields larger beam intensities and is often the best choice for H↘− ion beams. Best sources of the Lamb‐shift type produce currents ≥1μA with proton beam polarizations ≥0.7. Intensity increases of up to a factor of 3 may be possible by improving the present technology, but progress will be difficult to achieve.