The importance of communication skills for well-being and self-realization is widely accepted. Despite that, research on assertiveness and assertiveness training has declined significantly in recent decades. Consequently, traditional training does not consider the most recent novel technologies used to spread psychological interventions. This study proposes the development of ComunicaBene: a guided Internet-based imagery intervention to promote assertiveness. Moreover, it describes the study protocol for a randomized control trial to investigate the intervention’s efficacy and acceptability. Participants will be randomly assigned to an experimental (ComunicaBene) or waitlist control condition. ComunicaBene consists of different online training modules corresponding to three phases: psychoeducation, imaginative exposure, and in vivo-exposure. Each module provides participants with theoretical and practical content about needs, emotions, communication style, and assertiveness. Moreover, during the program, every student is supervised by a Tutor. Participants in the control condition will be included in a waiting list. Primary and secondary outcomes will include changes in assertiveness, well-being, emotional awareness, worry, and rumination. Outcomes will be assessed at pre- and post-intervention, and via a 6-month follow-up. We expect that the results will support the efficacy of ComunicaBene as an innovative, scalable, affordable, and acceptable intervention to spread assertive training through the Internet and among a broad population.