Preventing crime before it happens? This enticing narrative is no longer just science fiction. Computer-aided systems designed to predict criminal behaviour are used worldwide. The author explores the effects of this technology on society from a legal and criminological perspective. She concludes that the technology undermines various constitutional guarantees and poses considerable risks to the rule of law. If the technology is used unreflectively, crime control threatens to move into self-imposed algorithmic thoughtlessness. The book concludes with a proposal for minimum requirements to prevent such developments.