This article describes the theoretical background, origins, and development of a new clinical service for intervention in the putatively prodromal phase of schizophrenia and other psychotic disorders. Establishing such a service required examination of conceptual issues such as the meaning of the prodrome in psychosis and its association with risk of subsequent psychosis, and of practical issues related to identifying prodromal patients in the community and engaging them in monitoring and treatment. Patients' needs, timing, and mode of treatment had to be considered. Preliminary data from the service's 20-month pilot phase are presented to help inform these issues.