Objective: To examine whether digital marketing strategies are more strongly associated with energy drink use than other marketing and whether Theory of Planned Behavior (TPB) constructs mediated the effects of digital marketing on energy drink use. Design: A cross-sectional online survey using the TPB was administered in 2016. Setting: Illawarra region of New South Wales, Australia. Participants: A total of 359 young adults aged 18–24 years completed the survey. Participants were mainly students. Main Outcome Measures: Relative impacts of digital and other marketing on energy drink use and the mediating effects of TPB constructs: attitudes, subjective norm, and perceived behavioral control. Analysis: Stepwise regression analysis was employed to compare the effects on energy drink use from digital and other marketing. Mediation analysis was used to examine the mediating effects of the TPB constructs. Results: Digital marketing was more strongly associated than other marketing with young adults’ energy drink use. Attitudes, subjective norms, and perceived behavioral control mediated the effects of digital marketing on energy drink use. Conclusions and Implications: The marketing of unhealthy food and beverages such as energy drink products on the Internet requires greater scrutiny. Future interventions may focus on strategies to attenuate young adults’ attitudes toward energy drinks, denormalize energy drink use, and strengthening self-efficacy to reject energy drinks among this age group.