Individuals who develop schizophrenia often suffer long standing deficits. All too often available treatments remain palliative and do not improve the long-term course of illness. The neurobiological deficits associated with the onset of schizophrenia may be most active and damaging in the early stages of this life long illness, a fact which has shifted the focus of research and clinical work toward the early or prodromal stages of this disorder. Results from limited studies suggest that early intervention may lead to a better prognosis. Early interventions that could delay or prevent the onset of psychotic illnesses have obvious public health implications and rely on being able to identify true prodromal patients. The Structured Interview for Prodromal Symptoms and the Scale of Prodromal Symptoms are assessment instruments developed for operationally defining diagnosis and for quantitatively rating symptom severity for patients prodromal for psychosis.