This monograph explores the mechanisms and timing of possible etiologic events that contribute to fetal and neonatal neurologic injury. The report presents evidence that most cases of cerebral palsy are a result of multifactorial and unpreventable causes that occur during fetal development or in the newborn after delivery, and not a result of an isolated intrapartum hypoxic event. The report contains a set of criteria that may be used to define (or rule out) an acute intrapartum hypoxic event sufficient to cause or suggest cerebral palsy.