Three studies were conducted to investigate dispositional and environmental factors related to alcohol consumption during 21st birthday celebrations, and test an internet-based intervention designed to reduce alcohol consumption during 21st birthday celebrations (21BDCs). Results of Study 1 indicated the majority of alcoholic beverages (79.3%) are consumed rapidly. Rapid consumption was positively related to drinking history and normative perceptions, and negatively related to perceptions of behavioral control. The relation between sociocultural beliefs and rapid consumption are mediated by normative perceptions and perceptions of behavioral control. The major objectives of Study 2 were to explore: a) 21BDC planning behaviors and the physical and social 21BDC environment, b) the relation between intoxication and planning behaviors, celebratory behaviors, and the 21BDC environment, and c) the frequency of various alcohol-related negative outcomes. Results indicate 26.4% of the participants exceeded an eBAL of .26. Intoxication during 21BDCs is enabled by the availability of free drinks, and having a friend to look after oneself or monitor alcohol consumption does not lead to lower levels of intoxication. The most frequent negative outcomes were hangovers, blackouts and vomiting, with 50% of celebrants experiencing at least one of these outcomes. Study 3 tested a web-based intervention designed to reduce intoxication and negative outcomes during 21BDCs. The intervention was implemented four weeks before the 21st birthday, was designed to: a) change perceptions of drinking norms during 21st birthday celebrations, b) increase perceptions of behavioral control over alcohol consumption, and c) counter social pressures to consumer alcohol during the weeks leading up to the celebration. Results indicated no significant reductions in number of alcoholic beverages consumed, intoxication or negative outcomes, as compared to a traditional 21st birthday card intervention and no-intervention controls. While students were not motivated to implement many of the suggested harm-reduction strategies, there was a significant increase in the consumption of food and non-alcoholic beverages among participants receiving the web-based intervention. Development and implementation of effective interventions to reduce intoxication during 21BDC remains a significant challenge. / Ph. D.