In a criminal justice system in which almost every adjudicated defendant, regardless of age, pleads guilty, it becomes important to understand the decision-making process underlying this choice. In the present research, we examined how age (juvenile vs. young adult), guilt versus innocence, and plea comprehension influenced the decision to plead guilty and the underlying plea rationale. We found that whereas age did not affect willingness to plead guilty when participants were asked to assume guilt in a hypothetical scenario, juveniles were more than twice as likely as young adults to plead guilty when asked to assume innocence. In addition, consistent with past research and developmental theory, juveniles were significantly less likely than adults to consider the short- and long-term consequences of the decision, and to understand and appreciate plea-related information. We also found that legal knowledge, after controlling for age, was positively (albeit weakly) related to plea decisions, but only for guilty participants. Implications for juveniles and adults involved in the criminal justice system, as well as wrongful convictions, are discussed.