Electron spin resonance (ESR) spectroscopy can be used as an alternative to thermoluminescence in dating geological or archaeological materials. This arises because ESR spectroscopy specifically detects species containing unpaired electrons which is characteristic of fragments, formed by incident ionizing radiation, that may be trapped in rigid materials. A brief outline of the technique and of the type of information that it provides is given with special reference to the problems that arise in dating procedures. (See also <b>AATA</b> <i>16-842</i> and <i>18-1583</i>) -- AATA