<p>To overcome the modern environmental challenges, the European Green Deal has set a clear vision for transition towards the Circular Economy (CE), aiming to transform the European Union (EU) into a resource-efficient and competitive economy. To achieve this transition, the EU has recognized the importance of innovation in accelerating circularity at all levels by building, through the innovation process, new and suitable to each case CE models. Lately, a particular innovation model has been recognized by the literature and the practitioners as a strong answer in building and implementing CE models, named Open Innovation (OI). OI contributes mainly by promoting collaborations and by the intensification of knowledge, solutions, and know-how sharing between the collaborators, while traditional closed innovation limits the innovation process to a closed environment. CE at all levels and sectors has been significantly researched throughout the last decades, qualitatively and quantitatively. On the other hand, regarding OI, the research may not be as thorough as in the case of CE themes, but it has also been researched significantly. Focusing on CE models implementation through OI, it is a recent phenomenon, and little is known about the integration of the two themes. The subject of this paper is to review the existing literature on implementing CE models via OI, providing the reader with substantial insights into current practices, barriers, and prospects of the selected approach. Towards that end, a systematic literature review is being carried out, focusing specifically on the meeting point of CE and OI, as a newly introduced subject in research and practice. The vast scope of CE is categorized using the prevalent three implementation levels approach: macro, meso, and micro level, to organize both the research work and the conclusions. Key aspects of OI include the organization’s OI capacity, referring especially to culture, organizational structure, and practices. This review aims to collect and highlight insightful information on both research and practice, supporting the work of policy makers, decision makers, and executives or innovation managers in public or private organizations that are engaged with the transition towards a circular economy, as well as the research community surrounding both CE and OI. Research gaps will also be pointed out, as well as new directions for future research on both subjects.</p>