PIP: North American and western European cultures are more permissive than they were before World War II about the increased incidence of teen sexual activity. Societies may be more open and teens are having more premarital sex than they used to, but they surely are not using contraception as often as they should. As such, there is a great deal of unintended and unwanted teenage pregnancies, especially in the US. Even the threat of contracting and/or transmitting HIV has not caused heterosexual youths to change their sexual or contraceptive behaviors. The authors conceptualize explanations for this lack of adolescent behavioral change, including procedures designed to identify deficiencies and to bring about necessary changes in contraception-relevant information, motivation, behavioral skills, and situational constraints. Examples of successful intervention programs are outlined. Sections consider the incidence of premarital intercourse, contraceptive use, and unwanted pregnancies; contraceptive neglect; unintended and unwanted pregnancies; and why teenagers have unprotected sexual intercourse. The conceptual framework of intervening to prevent unwanted teenage pregnancies is presented in sections on providing improved contraceptive information, increasing precontraceptive motivation, improving contraceptive skills, altering situational factors which inhibit contraception, and evaluation research.