A new development in archaeological chronology involves the use of far travelled volcanic ash which may form discrete but invisible layers within a site's stratigraphy. Known as cryptotephra, these horizons can provide isochrons for the precise correlation of archaeological records at single moments in time, removing, or at least significantly reducing, temporal uncertainty within inter-site comparisons. When a tephra can be dated elsewhere, its age can be imported between records, providing an independent check on other dating methods in use and valuable age estimates for difficult to date sequences. The use of cryptotephra layers to date and correlate palaeoenvironmental archives is well established and there exists a wealth of tephra compositional data and regional tephrostratigraphic frameworks from which archaeological cryptotephra studies can benefit greatly. Existing approaches to finding and analysing cryptotephra are easily adapted to archaeological sequences, so long as the often complex nature of archaeological stratigraphies and sediment taphonomy are borne in mind.