Drinking, smoking, and drug use are symbolic behaviors for young people, often involving a claim for adult status, and set against a "social clock" of expectations about appropriate behavior for a given age. Use is set in a social world of youth sociability, which young people strive to control themselves. Hence, it is difficult to prevent or delay use through adult-run institutions such as schools. Youth-oriented prevention initiatives succeed best when in tune with general social trends, so that youth cannot so easily feel hypocritically singled out. Regulatory approaches that apply to all have had some success in limiting and shaping youthful use and problems. Well-evaluated trials of efforts to insulate youthful use from harm are needed.