<p>We are currently amid rapid environmental, social, political and economic change. These changes have resulted in negative planetary and societal impact. However, efforts to adapt to this change are typically slow and incremental and do not support systemic change towards a more sustainable future. There is a need for coherent action across all levels of society to stop the rapid degeneration of our planet and society. One way to increase coherent action is by bringing deeper awareness and understanding to the concept of synergy. Whilst the term synergy is often used, there is a lack of understanding of what it really means both conceptually and in its application. This paper addresses this gap through an integrative review, covering 14 disciplines. We identify three key attributes of synergy, highlighting its magnitudes, spatial and temporal scales, and the possibility for both positive and negative synergy. The findings also involve three broad conceptual understandings of synergy—synergy as outcome, synergy as processes and synergy as perceived wholes, each with strengths and limitations. Approaching synergy as outcome is useful in informing future actions. Approaching synergy as processes and synergy as perceived wholes, has the potential to maximise efficient use of resources, engender greater connectivity, enhance creativity, inform strategic planning for enhancing governance conditions and policy impact and support systemic change. To our knowledge, this review is the first to bring together a comprehensive understanding of synergy and has implications for cross-disciplinary research and practice, particularly to those working with change in large, complex systems.</p>