This book examines the early identification of children and adolescents with mental health and substance use problems in order to provide guidance, tools, and resources for early identification -- including a compendium of the most developmentally, culturally, and environmentally appropriate screening instruments. The U.S. Preventive Services Task Force, which evaluates the evidence on the efficacy of various preventive practices, has recommended screening adolescents for depression in primary care; however, it has not yet reviewed the evidence for general, multi-condition screening instruments, such as those discussed in this book. However, it is likely that many families -- especially those whose children fall into groups at elevated risk for mental health or substance use problems -- would prefer to know as soon as possible if their child or adolescent shows indications of these problems. Early identification and intervention would allow caregivers to promptly address any identified problems. Programs and services for youths who are at elevated risk for mental health and substance use problems should, as much as possible, offer caregivers the opportunity to identify any such problems. Because caregivers are the decision makers for their children, the guide emphasises that informed parental consent must always be obtained before any formal identification or screening process is conducted; it also reinforces that parental involvement from the beginning is appropriate and encouraged.