The ability of Industry 4.0 to help solve complex economic and social problems and implement complex concepts is assessed. Currently, one of the greatest challenges is the integration of the circular economy (CE) into real business practices. However, the link between these two ideas is not fully recognised, causing an interpretative dilemma. Therefore, the aim of this paper is to identify the relationships between the CE and Industry 4.0. For this purpose, we performed a systematic literature review and content analysis of selected articles indexed in Scopus, Web of Science, ScienceDirect, and EBSCO. In total, 32 papers published during the period 2017-2020 were analysed. The findings show a one-way relationship, i.e., Industry 4.0 leads to a CE, and a two-way relationship, indicating synergy between these concepts. The key spheres of the CE in terms of Industry 4.0 are the recycle and reuse strategy applied in smart production and a sustainable supply chain. This study demonstrates the importance of company (micro) and industry (meso) levels as application areas. The most promising digitalisation tools of Industry 4.0 are the Internet of Things (IoT) and Big Data Analytics. The article concludes with the limitations of the study and a formulation of directions for future research.