The purpose of this exploratory, sequential mixed-methods study was to describe resident assistants' (RAs) perceptions of their behaviors when dealing with situations involving alcohol and underage, undergraduate resident-students. Specifically, Ajzen's (1985) Theory of Planned Behavior (TPB) was used to analyze RAs' reports of their behaviors as they related to situations involving alcohol. Ajzen (1985) theorized that people behave in different ways given a variety of factors that influence their intention to behave. In this study, situations involving alcohol included in any circumstances in which alcohol was present or otherwise involved, such as when an RA encountered students consuming alcohol or apparently intoxicated students (e.g., exhibiting behaviors such as difficulty walking or slurred speech, which are ordinarily associated with consuming alcohol). Twenty RAs from seven colleges and universities in one northeastern state completed the Internet-based qualitative survey, which consisted of open-ended questions intended to gather RAs' reports of their behaviors in situations involving alcohol and underage, undergraduate resident-students. Procedures associated with qualitative research were used to analyze the data, develop 18 qualitative findings, and develop the quantitative instrument. One hundred thirty two RAs from the same institutions completed the Internet-based quantitative survey, which consisted of 143 close-ended items intended to determine the frequency with which RAs used various behaviors in situations involving alcohol and the reasons for those behaviors. Analysis of the data yielded 21 relatively distinct behaviors that RAs reported using in situations involving alcohol, which grouped into three themes: (a) ensuring the safety of students, (b) reporting and documenting the situation, and (c) informing authority about or obtaining support. Additionally, the attitudes, subjective norms, and perceived behavioral controls RAs reported that drive their behavior grouped into two issues: (a) ensuring the safety of students and the broader campus community and (b) contending with role conflict and ambiguity. Finally, there were 11 significant differences between behaviors reported by RAs at public institutions and RAs at private ones. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]