There have been two major criticisms of the past literature on youths' capacities: concerns about what capacities have been studied and how the studies have been designed. The first criticism suggests that methodological weaknesses in sampling and measurement limit the conclusions that can be drawn from prior research. The second criticism holds that prior research has been limited by a focus on adult criteria for competence, overlooking additional developmental factors that might affect juvenile capacities. Generally, two broad goals define the structure of an empirical inquiry into juveniles' capacities as defendants: identifying the capacities and capabilities relevant to the law, specifically adjudicative competence, and identifying juveniles' performance under a variety of relevant conditions and contexts. A number of methodological issues arise when designing research to meet these goals. The complexity of sampling and research design requires attention to the characteristics of age-based comparisons within the justice system and comparison samples from the community. The potential contributions of cross-sectional, longitudinal, and intervention designs need to be identified. The need for improved ecological validity by incorporating contextual factors at multiple levels (personal, relational, and systemwide) should be taken into account. Directions for the measurement and analysis of competence-relevant capacities also must be identified. Studies should include improved measures of context-specific capacities as well as general measures of the same capacities; use multiple methods of assessment that go beyond traditional self-report methods; and incorporate several approaches to data analysis. 51 references