The science of pain assessment for infants and children has grown substantially in the past several decades to the point that valid and reliable methods for pain assessment are available for use in clinical settings. Accurate pain assessment requires consideration of children's developmental level, type of pain experienced, history and context of pain, family influences, and interaction with the health care team. Research is needed to improve the sensitivity, specificity, and generalizability of pain-assessment tools and to more fully incorporate contextual factors into the objective assessment process. Finally, the improvement of pain assessment in the clinical setting can be viewed as a patient care quality issue, and continuous quality improvement methods can be used effectively to incorporate pain assessment as an integral component of every infant's and child's health care.