Cerebral palsy (CP) is the most common cause of physical disability in children. CP currently has no cure and there are only few interventions to prevent the development of disability. There are four principal complications of pregnancy or birth that can damage the developing brain and lead to CP: preterm birth, fetal growth restriction, infection during pregnancy and severe hypoxia-ischemia at birth. Umbilical cord blood (UCB) cells are a very promising therapy for the treatment of CP. While UCB therapy for juveniles with CP is currently being assessed in clinical trials, very little is known about their mechanisms of action or which cells found in umbilical cord blood protect against and/or repair brain injury. In this chapter, we first explore the complications that can lead to perinatal brain injury. We then discuss the different cell types found in UCB and the specific properties that make each of them individually attractive therapeutic candidates for treatment of perinatal brain injury. While UCB holds much promise as a therapy for CP, it is imperative that more research is conducted to understand how the different cell types found in UCB can protect against brain injury in order to design more effective and targeted therapies.