Sleep disorders are common in both children and adults. Untreated sleep disturbances pose significant, adverse daytime consequences and place individuals at considerable risk for adverse health outcomes. Nurses are well positioned to assess and intervene with sleep disorders because they care for people across all cultures, age groups, and health conditions in community and clinical settings. There is widespread agreement among clinical and research experts that sleep assessment should be an integral component of all health assessment, with the specific focus and scope dependent on the situation. This chapter familiarizes nurses with evidence-based approaches to the assessment of sleep. It addresses the basic components of sleep assessment for children and adults, including obtaining sleep-related history, detailed sleep evaluation, and physical examination. The chapter includes information on self-report and objective sleep measurement and resources on sleep assessment for nurses, patients, and their families.