Caries detection currently occupies a good deal of attention in the arena of dental research for a number of reasons. In searching for caries detection methods with greater accuracy than conventional technique researchers have used a variety of optical methods and have increasingly turned to the use of lasers. Several laser-based methods have been and are being assessed for both imaging and disease quantification techniques. The phenomenon of fluorescence of teeth and caries in laser light and the different effects produced by different wavelengths has been investigated by a number of workers in Europe. With an argon ion laser excitation, QLF (Quantified Laser Fluorescence) demonstrated a high correlation between loss of fluorescence intensity and enamel mineral loss in white spot lesions in free smooth surface lesions, both in vitro and in vivo. Recent work with a red laser diode source (655 nm), which appears to stimulate bacterial porphyrins to fluoresce, has demonstrated that a relatively simple device based on this phenomenon can provide sensitivity and specificity values of the order of 80% in vitro and in vivo for primary caries at occlusal sites. In vitro studies using a simulated in vivo methodology indicate that the device can produce sensitivity values of the order of 90% for primary caries at approximal sites.