A Workshop was held which invited a range of speakers to consider separately the different diagnostic tools presently available for the detection of caries and then the various applications to which these tools can be put. Each presentation was followed by a vigorous discussion period. It was concluded that there is no one single method suitable for all anatomical sites and degrees of caries and that the requirements for epidemiological surveys, clinical trials and individual patient care are different. The choice of appropriate diagnostic technique(s) should be made, in each situation, on the basis of published performance data which has to be regularly re-evaluated due to the pace of change.