Underage drinking is common among Swedish adolescents and is related to problems for individuals, families, and society. From a public health perspective, it is of great importance that knowledge be gained about alcohol prevention. The overall aim of this thesis is, within the context of a national support program for NGOs, to study parents, a parental support program, and adolescents with regard to preventing underage drinking.  The Swedish National Board of Health and Welfare (NBHW) has a government commission to distribute funds to non-governmental organizations (NGOs) for alcohol and drug prevention efforts. Study I of the thesis describes and analyses this program with a special emphasis on research and development for an evidence-based practice. It is a research strategy case study with 135 projects and 14 embedded in-depth studies. The results reveal that this program to support NGOs has been successful in engaging a wide range of NGOs in prevention efforts. A trustful partnership between practitioners, national agencies, and researchers has also been developed, which has improved the quality and results of the different projects. Studies II, III, IV, and V all used data from a longitudinal questionnaire study with parents and adolescents within one of the 14 in-depth studies: the study of IOGT-NTO’s parental program Strong and Clear. Additional data, such as telephone interviews and other parental questionnaires, are also used.  Study II aims to analyse the significance of socio-demographic factors for parental attitudes and behaviour regarding adolescent alcohol consumption to see if any group of parents is especially important for intervention efforts. The results showed that fathers were more likely than mothers to have non-restrictive attitudes towards underage drinking and to have children who had drunk or tasted alcohol at home. Study III examines reasons for non-participation in the program. Parents with a low educational level were found more likely to be non-participants than highly educated parents. When parents stated their reasons for non-participation it emerged that they did not perceive a need for the intervention and that there were practical obstacles to their participation. Study IV is an effect study of Strong and Clear and showed that the program contributed to maintaining parents’ restrictive attitude toward underage drinking, postponing alcohol debut, and preventing drunkenness among the adolescents. Study V, only presented in the thesis, examined parents’ perceptions about Strong and Clear. Parents primarily thought it had led to their speaking more often about alcohol with their children, and had been a help in this conversation. Many also stated that the program had influenced their ability to set limits for their children. The school and IOGT-NTO were considered as suitable providers of Strong and Clear. This thesis showed that a national support program for NGOs including research and development contributes to a more evidence-based public health practice.