Although complementarity achieved by combining multiple renewable energy sources (RES) is an important method to increase shares of RES, it is often overlooked in policy prescriptions supporting an energy transition. Complementarity can be implemented by multiple actors, however there has been little attention to which actors are involved, and their roles. A systematic review was conducted to provide an overview of the state of academic literature on the topic of combinations of multiple RES and the involvement of multiple associated actors. The sample included 78 articles using a range of methodologies to analyze varying combinations of wind, solar, bioenergy, hydro, geothermal, and ocean energy, alongside combinations of traditional, new, and supporting energy actors. Studies included contextualized (location specific) agent-based, techno-economic, economic, business model, and qualitative analyses, and decontextualized reviews, agent-based, and optimization models. Multi-actor complementarity is being addressed by diverse disciplines in diverse contexts globally, across a range of geographic scales. The majority of studies focus on solar-wind, although more diverse RES combinations were found in contextualized studies. New actors usually participate alongside traditional system actors. More attention to supporting actors is required. Findings highlight the need for further research beyond the technical benefits of combining multiple RES, to explore the roles of various actors. This can be accomplished by incorporating more context in studies, for example, using the substantial existing body of data and research, and by including a greater range of RES combinations, and incorporating more perspectives of associated actors. •Systematic review to understand actor involvement in complementarity of renewables.•The sample represents diverse disciplines with various methodologies.•The topic is being studied both in and out of geographical context, at varying scales.•Wind and solar were most common, but more diverse combinations are found in context.•Traditional and new actors found across studies; supporting actors require attention.