Two subcommittees of the DSYDS - the Jurisdictional Case Studies (JCS) Subcommittee and the Linked Administrative Data (LAD) Subcommittee - have focused on addressing this knowledge gap. Their study of this issue has two goals. One goal is to identify the successes and challenges associated with cross-system collaboration, identify best practices for dual system youth, and develop a tool to collect and report such information in a consistent and representative way. The second goal is to provide insight into the incidence of dual system involvement and describe key characteristics (e.g., race, gender, class, ethnicity, and sexual orientation) and trajectories (e.g., timing/type of encounters with the systems) of this population, as well as to propose a method for generating a national estimate of dual-system youth. In pursuing these goals, the JCS Subcommittee reviewed data from jurisdictions that are participating in the Georgetown University Center for Juvenile Justice Reform’s Crossover Youth Practice Model (CYPM). This effort enabled the identification of successes and challenges in cross-system collaboration for dual-system youth from a broad range of jurisdictions and stakeholders. The LAD Subcommittee focused on the analysis of linked administrative data drawn from Cook County, Illinois; Cuyahoga County, Ohio; and New York City. This effort produced dual-system youth incidence rates and a description of their characteristics, so as to test the use of linked administrative data that can produce a national estimate. The collective work of these subcommittees is summarized in this report, representing the culmination of 3 years of work.