The digitalization of greater society has permeated organizations, where managers are reassessing how internal communication is practiced and defined, particularly in the context of public relations and strategic communication. These changes were already underway before the COVID-19 pandemic, which strongly highlighted the importance of effective internal communication. Now more than ever, digital transformation is profoundly affecting internal communication, yet there are substantial gaps in our understanding of the current situation. This study aims to identify and provide an overview of the research in the area through a systematic review of 77 research studies published in 52 journals between the beginning of 1990 and November 2022. The findings reveal the evolution of research on digital internal communication and highlight geographical, theoretical, and methodological gaps that should be addressed in future work. First of all, the effectiveness of different internal communication channels needs to be thoroughly researched. This includes the effectiveness of collaboration tools and platforms, the influence of channels that enable remote work, and the significance of gamification and an interactive communication approach. Also, digitalization in internal communication should be given more attention from a social perspective, underlining the effects of internal communication digitalization on employees and their satisfaction as well as employee concerns with privacy, control, and other ethical dilemmas regarding easy accessibility to data. Finally, digitalization of internal communication should be researched as a transformation process within organizations, which has not yet been done. •Systematic review of digital internal communication.•Effectiveness of IC channels needs to be thoroughly researched.•Digitalization in IC should be explored from a social perspective.•Digitalization of IC should be researched as a transformation process.