This narrative review summarizes the empirical literature on children's competence for consent and assent in research and treatment settings. Studies varied widely regarding methodology, particularly in the areas of participant sampling, situational context studied (e.g., psychological versus medical settings), procedures used (e.g., lab-based vs. real-world approaches), and measurement of competence. This review also identified several fundamental dilemmas underlying approaches to children's informed consent. These dilemmas, including autonomy versus best interests approaches, legal versus psychological or ethical approaches, child- versus family-based approaches, and approaches that emphasize consent versus those that emphasize assent, have implications for the measurement of children's competence and interpretation of findings. Recommendations for future research in the area of children's informed consent include the use of diverse samples and control groups, development of multidimensional and standardized measures of competence, utilization of observational methods and longitudinal designs, examination of noncognitive aspects of children's competence, and comparison of children's competence for treatment and research decisions.