There is no single definition of the terms "runaway youth" or "homeless youth." However, both groups of youth share the risk of not having adequate shelter and other provisions, and may engage in harmful behaviors while away from a permanent home. These two groups also include "thrownaway" youth who are asked to leave their homes, and may include other vulnerable youth populations, such as current and former foster youth and youth with mental health or other issues. Youth most often cite family conflict as the major reason for their homelessness or episodes of running away. A youth's relationship with a step-parent, sexual activity, sexual orientation, pregnancy, school problems, and alcohol and drug use are strong predictors of family discord. The precise number of homeless and runaway youth is unknown due to their residential mobility and overlap among the populations. Determining the number of these youth is further complicated by the lack of a standardized methodology for counting the population and inconsistent definitions of what it means to be homeless or a runaway. Estimates of the homeless youth exceed 1 million. Estimates of runaway youth-including "thrownaway" youth (youth asked or forced to leave their homes)-are between 1 million and 1.7 million in a given year. From the early 20th century through the 1960s, the needs of runaway and homeless youth were handled locally through the child welfare agency, juvenile justice courts, or both. The 1970s marked a shift toward federal oversight of programs that help youth who had run afoul of the law, including those who committed status offenses (i.e., running away). In 1974, Congress passed the Runaway Youth Act of 1974 as Title III of the Juvenile Justice and Delinquency Prevention Act (P.L. 93-415) to assist runaways through services specifically for this population. The federal Runaway and Homeless Youth Program (RHYP) has since been expanded through reauthorization laws enacted approximately every five years since the 1970s, most recently by the Reconnecting Homeless Youth Act (P.L. 110-378) in 2008. Funding authorization expired in FY2013, and Congress has continued to appropriate funding for the act: $114.1 million was appropriated for FY2015. The Runaway and Homeless Youth program is made up of three components-the Basic Center Program, Transitional Living Program, and Street Outreach Program. The Basic Center Program provides temporary shelter, counseling, and after care services to runaway and homeless youth under age 18 and their families. The BCP has served approximately 31,000 to 36,000 annually in recent years. The Transitional Living Program is targeted to older youth ages 16 through 22 (and sometimes an older age), and has served approximately 3,000 to 3,500 youth annually in recent years. Youth who use the TLP receive longer-term housing with supportive services. The Street Outreach Program provides education, treatment, counseling, and referrals for runaway, homeless, and street youth who have been subjected to or are at risk of being subjected to sexual abuse and exploitation. Each year, the SOP makes hundreds of thousands of contacts with street youth (some of whom have multiple contacts). Related services authorized by the Runaway and Homeless Youth Act include a national communication system to facilitate communication between service providers, runaway youth, and their families; training and technical support for grantees; and evaluations of the programs, among other activities. The 2008 reauthorizing legislation expanded the program, requiring HHS to conduct an incidence and prevalence study of runaway and homeless youth. To date, this study has not been conducted; however, efforts are underway among multiple federal agencies to collect better information on these youth as part of a larger strategy to end youth homelessness by 2020.