Using on-line handwritten signature verification (HSV) for authentication is attractive because of the long–standing tradition of its use in many common authentication tasks. HSV may be considered superior to many other biometric authentication techniques, for example fingerprints or retinal patterns, which are more reliable but also more intrusive. Furthermore, they require special and relatively expensive hardware to capture the image. This paper presents a review of some on-line HSV techniques that have been reported in the literature. The paper also lists some commercial products that are currently available and discusses a number of applications of HSV.