A primary goal of this study was to propose a methodology for estimating a nationally representative incidence rate of dual system youth. Collectively, our research team reviewed the various options and concluded that producing a nationally representative incidence rate of dual system youth required the use of linked administrative data. Westat conducted a landscape assessment of child welfare and juvenile justice data using extant information available to assess the viability of accessing the data needed for such a study (see Chapter 8). These findings, in turn, informed the methodology recommended in Chapter 9. These processes were informative, underscoring the need to access administrative data while highlighting issues related to doing so. In this chapter, we provide a brief summary of the proposed design and key issues related to using child welfare and juvenile justice data at the national level.