In recent years, predictive instruments have increasingly been used to support police work. By means of standardized assessment procedures, these instruments are intended to evaluate the risk posed by an individual of committing criminal offenses in the future. The resulting assessments enable the police to allocate their resources for crime prevention in a more targeted manner. Maja Werner examines the legal requirements that must be observed when such an instrument is developed and applied for police purposes. To this end, she first outlines the fundamental structures underlying the legal framework of police decision-making and analyzes how predictive instruments can be situated within this framework. Building on this classification, she identifies the constitutional and administrative law standards governing police decision-making processes and shows how these standards apply to predictive instruments. This analysis already demonstrates that many of the existing legal requirements are not designed to address. This analysis already demonstrates that many of the existing legal requirements are not designed to address complex data processing procedures for predictive purposes. For this reason, the author then develops these legal requirements in line with their underlying constitutional and rule of law objectives. In doing so, she develops legal guidelines for the design of predictive instruments for police purposes and their application in police practice.