Delirium is a prevalent and underrecognized syndrome of acute brain dysfunction in critically ill children, associated with significant morbidity, mortality, and healthcare expenditure. This chapter presents known risk factors, preventive measures, potential precipitants, pathophysiological conceptualizations, pediatric-validated screening and assessment tools, and interventions for addressing this serious condition in youth. Systematic, multidisciplinary, and family-centered approaches to care are presented as effective strategies for promoting positive outcomes. Patient populations at increased risk for delirium are outlined, including neonates and young children, youth with developmental disabilities, patients with comorbid neuropsychiatric illnesses such as catatonia and autoimmune encephalitis, children with acquired brain injury, and patients approaching the end of life. Because delirium may arise in the context of medical illnesses across the full spectrum of organ systems and under the purview of providers from diverse medical disciplines, the condition represents a clear opportunity for neuropsychiatrists to serve as leaders, teachers, and advocates for collaborative care and advancements in the field.