Traditionally, recommendations and procedures for obtaining consent and assent from children to participate in research have varied somewhat from institution to institution. At least some of this inconsistency can be attributed to a lack of consensus on what consent means when applied to individuals less than 18 years of age. Developmental theories provide some rationale for reconsidering the arbitrary age limit of 18 years for informed consent. In this article, the concepts of consent and assent are discussed relative to developmental characteristics of children and adolescents and implications for consent and assent procedures are discussed.