Alcohol and/or substance use among college students is a serious public health issue. In Oman, studies addressing college student's alcohol and/or substance use are limited. The purpose of this study was to identify knowledge, attitudes, subjective norms, self-efficacy, and perceived behavioral control associated with alcohol and/or substance usage patterns among Omani college students (OCSs); identify behavioral intentions for alcohol and/or substance use among OCSs; and facilitate the development of culturally relevant evidenced-based interventions for Omani young people by communicating study findings to policymakers and healthcare program leaders. A cross-sectional design used an online survey completed by college students from Oman higher education institutes (HEIs) in academic year 2016-2017. One hundred and eighty-two males (45.2%) and 224 females (54.8%) reported 30-day prevalence rates of 3.2% and lifetime prevalence rates of 15.9% for alcohol and/or substance use. Attitudes, subjective norms, and self-efficacy significantly predicted OCSs' alcohol and/or substance use behavioral intentions (p < 0.05). Perceived behavioral control was not a significant predictor. Socio-demographic factors (i.e., age, gender, father's educational level, family income, college type, region of permanent residence, and religiosity) were significantly associated with and predicted OCSs alcohol and/or substance use behavioral intentions (p < 0.05). Findings supported attitudes, subjective norms, self-efficacy, and perceived behavioral control as predictors for alcohol and/or substance use behavioral intentions among OCSs. Notably, alcohol and/or substance behavioral use intentions and behaviors of surveyed OCSs were influenced by their attitudes, subjective norms, and self-efficacy rather than by their knowledge of the health consequences. Secondly, OCSs reported a strong self-efficacy in their ability to avoid alcohol and/or substances; however, this did not translate to lower intentions. Public health professionals, educators, and policymakers should focus on influencing intentions and on strengthening OCSs' confidence to abstain from alcohol and/or substances. This can be accomplished by incorporating avoidance or refusal training skills into HEIs' existing evidence-based interventions for alcohol and/or substance use for OCSs. Incorporating this same skill training may yield further evidence about which TPB constructs public health professionals should include in the development of national alcohol and/or substance use prevention programs. [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.]