Book excerpt: A voice is much more than just a string of words. Voices, unlike fingerprints, are inherently complex. They signal a great deal of information in addition to the intended message: the speakers' sex, for example, or their emotional state, or age. Although evidence from DNA analysis grabs the headlines, DNA can't talk. It can't be recorded planning, carrying-out or confessing to a crime. It can't be so apparently directly incriminating. Perhaps it is these features that contribute to the interest and importance of Forensic Speaker Identification (FSI)