Cannabis (including marijuana, hashish, and other forms of tetrahydrocannabinol) is the most prevalent psychoactive substance used by adolescents in the USA (Coffey et al., 2002; Dennis et al., 2002a; Hall & Babor, 2000; Institute of Medicine [IOM], 1999; Kraus & Bauernfeind, 1998; SAMHSA, 2000a; Swift, Copeland, & Hall, 1998). In 2002, it was estimated that nearly one half of all adolescents in 12th grade in the USA had used cannabis; nearly 40% of those in 10th grade and close to 20% of those in 8th grade reported the same (Johnston, O'Malley, & Bachman, 2003). Although they have leveled off, the rates of adolescent cannabis use continue to be approximately twice as high as they were in the early 1990s (Johnston et al., 2003; SAMHSA, 2002). In addition, the number of adolescents starting use before the age of 15 grew throughout the 1990s, continuing a trend that has been unfolding since the 1980s, and its use and dependence are comorbid with a wide variety of psychological and behavioral conditions (reviewed at length in Dennis et al., (2002b)). Cannabis is the leading substance mentioned in arrests and emergency room admissions of adolescents in the USA, and the second leading substance mentioned in autopsies (Bureau of Justice Statistics, 2000; SAMHSA, 2000b, c, d). From 1992 to 1998, the number of adolescents presenting for treatment for cannabis use rose by 53%; currently over two thirds of the adolescents in publicly funded treatment are being seen for cannabis-related problems, with 80% being seen in outpatient settings (Dennis et al. 2003).