This guide provides suggestions and tips for improving services to youth and young adults across different agencies and domains. Young people with behavioral and mental health disorders have a wide range of needs related to health, education, employment, and safe housing. They may be served by several systems such as child welfare, juvenile justice, and vocational rehabilitation that may or not communicate and coordinate services. Young people may also have needs that are not specific to any system, such as learning skills in budgeting, self-care, and managing interpersonal relationships, to successfully transition to adulthood. Collaboration and teamwork are necessary, therefore, to provide services to youth successfully. One key to success is engaging young people in collaboration. The authors recommend that agencies and organizations develop system-level collaboration.